




















                                Program ASTROCLK

                Astronomical Clock and Celestial Tracking Program

                            with Celestial Navigation







                             by David H. Ransom, Jr.
                             Rancho Palos Verdes, CA





                                  Version  8947
                                November 19, 1989
   ASTROCLK Astronomical Clock and Celestial Tracking Program        Page i







                                TABLE OF CONTENTS




        ACKNOWLEDGEMENTS.........................................1
        INTRODUCTION.............................................2
        HARDWARE REQUIREMENTS....................................7
        PROGRAM OPERATION........................................10
           Required ASTROCLK Files...............................10
           Starting Program ASTROCLK.............................12
           Running Program ASTROCLK..............................13
        FUNCTION KEYS AND HELP...................................18
           F1 Display HELP Screens...............................18
           F2 Display Target Object EPHEMERIS....................18
           F3 Set Time and/or Date...............................18
              Read Hardware Clock................................19
              Set ALARM or INTERVAL TIMER Time...................19
           F4 Toggle Clocks ON or OFF............................19
              Enable Simulated Real Time.........................19
           F5 Set Target Coordinates.............................20
              Enter USNO Star Name or Number.....................20
              Search for Nearest USNO Star.......................20
              Search EXTERNAL STAR CATALOG by Name or ID.........20
              Search EXTERNAL STAR CATALOG by RA and DEC.........21
              Search EXTERNAL STAR CATALOG for Nearest Star......21
              Manual Target Data Entry...........................21
              Set Polaris Coordinates............................22
           F6 Set Local Coordinates..............................23
              Set Destination Coordinates........................23
              Set Local Conditions...............................23
           F7 Set Display Format.................................23
              Change Target Display Coordinates..................24
           F8 Precess Internal Star Database.....................24
           F9 DOS Shell..........................................25
              Execute Preset DOS Command.........................25
              Execute USNO Ephemeris (ICE or FA).................25
          F10 Celestial Navigation...............................26
              Setting Program Options............................26
          0-9 Select Display Window Mode.........................26
        SETTING PROGRAM OPTIONS..................................28
           Setting the DAYLIGHT FLAG.............................28
           Setting the ZONE CORRECTION...........................29
           Setting the COLOR FLAG................................29
           Setting the ICE/FA FLAG...............................30
           Setting the CALENDAR FLAG.............................30
           Setting the FILE NAMES and PATHS......................31
           Setting the PRESET DOS COMMAND........................33
        SETTING LOCAL/UT/TDT TIME AND DATE.......................34
           Setting the LOCAL/UT/TDT Time.........................36
   ASTROCLK Astronomical Clock and Celestial Tracking Program        Page ii


           Setting the LOCAL/UT Date.............................37
        SETTING LOCAL AND DESTINATION COORDINATES................39
        SETTING LOCAL CONDITIONS.................................43
        DUAL-TIME DISPLAYS.......................................44
        ALARM AND INTERVAL TIMER OPERATIONS......................46
           Using the ALARM Function..............................46
           Using the INTERVAL TIMER..............................47
           Linked ALARM & INTERVAL TIMER Operation...............48
        TARGET TRACKING DISPLAY..................................49
        TARGET OBJECT EPHEMERIS..................................53
        PRECISION TIME AND DATA DISPLAYS.........................55
           Precision Time Display #1.............................55
           Precision Time Display #2.............................57
           Precision Data Display #1.............................57
           Precision Data Display #2.............................58
           Precision Data Display #3.............................59
        PLANETARY DATA DISPLAYS..................................60
        MINOR PLANET SELECTION...................................64
           Entering Orbital Parameters...........................67
        CELESTIAL NAVIGATION.....................................69
           Setting UT TIME ZONE OFFSET...........................70
           Navigation by Dead Reckoning..........................73
           Celestial Navigation with Star Sights.................80
           Selecting USNO Navigational Stars.....................84
           Celestial Navigation Example..........................86
        SIDEREAL TIME AND EQUATORIAL COORDINATES.................90
        USNO COMPUTER EPHEMERIS PROGRAMS, ICE AND FA.............92
        USNO STANDARD NAVIGATIONAL STARS.........................95
        CONSTELLATIONS AND NAMES.................................97
        USING EXTERNAL STAR CATALOGS.............................101
        PRECESSION AND STELLAR MOTION............................104
        DATES AND THE GREGORIAN CALENDAR.........................106
        WHAT TIME IS IT?.........................................112
        PRECISION AND ACCURACY TESTS.............................118
           Compiler..............................................118
           Calendar Dates........................................119
           Julian Dates..........................................120
           Universal Times (UT and UTC)..........................120
           Terrestrial Dynamical Time (TDT, ET and Delta T)......120
           Atomic Times (TAI and A.1)............................121
           Sidereal Times (GMST and GAST)........................121
           Precession............................................122
           Solar Position Calculations...........................124
           Major Planet Position Calculations....................127
           Minor Planet Position Calculations....................128
           Celestial Navigation Calculations.....................128
           J2000.0 Internal Star Database........................130
        ASTROCLK MESSAGES AND ERRORS.............................131
           ASTROCLK Numbered Errors and Cautions.................131
           Other ASTROCLK, QuickBASIC and DOS Errors.............137
        A BRIEF EDITORIAL........................................139
        BIBLIOGRAPHY.............................................142
   ASTROCLK Astronomical Clock and Celestial Tracking Program        Page 1







                                ACKNOWLEDGEMENTS

             Few tasks of any consequence are accomplished unaided. For 
        ASTROCLK, in addition to the numerous references cited in the 
        BIBLIOGRAPHY, there are several individuals to whom special 
        thanks are due.
             Ward Harman, a retired engineer living near me in Palos 
        Verdes, California, has spent many hours testing and validating 
        the performance of various aspects of ASTROCLK, advising me of 
        errors when he found them, and making numerous suggestions with 
        respect to both style and substance.
             Steve Brewster, of Stony Ridge Observatory high above 
        Pasadena, California, has been most generous with his time, 
        advice, and encouragement. To all of that, he added a long and 
        fascinating evening at the Observatory where we were able to 
        experience firsthand the thrill of "real" astronomy using SRO's 
        30-inch reflector and which helped me to better understand how 
        ASTROCLK might be used in that environment.
             And to all of those interested astronomy and computer 
        enthusiasts who have called, written, or left messages for me on 
        my bulletin board system, my thanks for your kind words and 
        suggestions. Those letters and calls inform me that ASTROCLK is 
        being used in Europe, Hong Kong, Japan, Israel, and Australia in 
        addition to the United States and Canada. I must be doing 
        something right! ASTROCLK is now embarking upon its third year.
             Finally, and by no means least, my wife Vicki has been both 
        patient and supportive during the many hundreds of hours I have 
        spent hunched over one or another of my computers as ASTROCLK has 
        evolved from a simple sidereal clock to the complex program it is 
        today. It was her interest in, and curiousity about, astronomy 
        and the night sky which helped inspire my efforts in the first 
        place, and her encouragement has been essential during the years 
        that I have invested in ASTROCLK.

                                                November, 1989

                                                David H. Ransom, Jr.
                                                Rancho Palos Verdes, CA
   ASTROCLK Astronomical Clock and Celestial Tracking Program        Page 2



        INTRODUCTION

             Program ASTROCLK is an Astronomical Clock and Celestial 
        Tracking Program. ASTROCLK is free for non-commercial use. Use it 
        if you like it, discard it if you don't. There are no warranties 
        of any kind. If you wish to use ASTROCLK commercially, write for 
        license information. For information on how to obtain the most 
        recent version of the program, see the section A BRIEF EDITORIAL. 
        And now, on with the story ...
             Like many people, I have long been fascinated by the stars 
        at night and by things astronomical. But it was not until some 
        years ago, when I spent considerable time in the foothills of 
        Northern California, that I regularly saw the night sky without 
        the interference of city lights. There followed a heightened 
        interest in the stars and a desire to be able to recognize the 
        various constellations and important individual stars. Many 
        books, star charts, and cold winter nights later the age of the 
        Personal Computer dawned. Suddenly, I realized, I had a tool 
        which would enable me to figure out many of these things on my 
        own and practically in real time.
             Program ASTROCLK has evolved from a series of smaller 
        programs, each designed to calculate some little piece of 
        astronomical data which I needed or wanted for use with my hobby. 
        Each time that I needed still another bit of data in order to do 
        something, I'd search out the necessary formulae or methods and 
        write a new little program to automate the process. After a 
        relatively short period of time I discovered that I had literally 
        dozens of such small programs, but no single program was ever 
        sufficient to get me all the information I sought at a particular 
        time.
             Equally frustrating, none of the stand-alone programs 
        available or that I had written up to that point gave me the 
        information in real time, adjusted for my geographical location. 
        I always had to look up all the things I'd forgotten or run 
        a number of programs to get the data I sought. And to further 
        complicate things, there are an almost unbelievable number of 
        different methods for telling time, of which perhaps half a dozen 
        or so are useful to the casual astronomer or navigator. I finally 
        mastered the zone changes from Greenwich to Los Angeles, but 
        converting local time to sidereal time ("star time", if you 
        prefer) in my head has so far eluded me. Program ASTROCLK was 
        intended to solve all of these problems for me. While it is still 
        some distance from accomplishing that rather ambitious goal, it's 
        a very big step along the way. I'm starting to run out of 
        "necessary" features to add!
             As with any profession, astronomers and navigators have 
        developed a technical language all their own to describe the 
        phenomenae of time and celestial mechanics. Not only is this 
        language almost as complex as the science it seeks to describe, 
        but many seemingly common words carry definitions far divorced 
        from everyday life and our intuitive understanding of their 
        meaning. The amateur astronomer or layman can easily become 
        hopelessly confused, particularly as not all texts, 
        organizations, and related professions necessarily use precisely 
   ASTROCLK Astronomical Clock and Celestial Tracking Program        Page 3


        the same words or even the same definitions to describe a given 
        measurement or item of data. All too frequently the definitions 
        have changed over time, and sometimes they are even reversed from 
        one discipline to another.
             For my own understanding and entertainment, I have spent 
        considerable time researching the subject and attempting to 
        assemble a consistent set of computer programs and algorithms to 
        facilitate the practical use of my personal computers in 
        astronomy and navigation. Program ASTROCLK now represents a 
        continuing effort spanning almost two years and more than a
        thousand hours of work. I hope that effort is judged worthwhile.
             The advent of the truly portable personal computer has 
        served as an additional spur to these efforts so that I may have 
        the information at my fingertips no matter where I may travel. 
        There are moments when I wonder who is the slave and who the 
        servant.
             I have used many and varied sources and have made every 
        effort to assure the accuracy of the information and calculations 
        presented. However, I alone am responsible for the final outcome 
        -- along with any errors that may be discovered. My thanks to 
        those individuals who have taken the time to report problems and 
        suggest improvements. Without their interest and encouragement, I 
        doubt that ASTROCLK would have become what it is or that my 
        efforts would have continued.
             The first and most important order of business for any 
        astronomer or navigator is to know what time it is. For ASTROCLK, 
        I assume that the computer's internal clock has been set to the 
        correct local time, keeps reasonably good time, and that the 
        relationship between local time and Coordinated Universal Time 
        can be calculated or is known. To a high degree of accuracy, 
        what is now known as Coordinated Universal Time (UTC) was 
        previously called Greenwich Mean Time; there are those who still 
        insist on using the old name. The U. S. military forces, ever 
        adept at finding a different name for things we might otherwise 
        recognize, refer to UTC as Zulu Time. In the United States, the 
        National Bureau of Standards continuously broadcasts UTC on 
        stations WWV (Fort Collins, Colorado) and WWVH (Kauai, Hawaii); 
        the frequencies transmitted are: 2.5MHz, 5MHz, 10MHz, 15MHz and 
        20MHz (WWV only). Reception will vary depending upon the time of 
        day, geographic location, and current atmospheric conditions. In 
        Europe and in many places around the world, the BBC World Service 
        gives a time signal every hour which is synchronized with 
        Greenwich Mean Time, essentially identical with UTC.
             As an aside, I have noticed that the hardware clocks in my 
        computers maintain more accurate time than do the software clocks 
        (particularly with versions of MS-DOS prior to 3.xx). Further, 
        some programs which use high speed serial communications disable 
        the software clock during operation and the time errors can 
        become substantial. Other software can also suspend timekeeping 
        functions for brief intervals. On my Zenith Z-248 system (an IBM 
        AT-compatible), for example, use of the program BROOKLYN BRIDGE 
        (inter-computer communications) can introduce errors of tens of 
        seconds or more. I recommend that you first check the accuracy of 
        your software clock, the one that keeps track of time after you 
        begin using the computer, over a period of several hours. An easy 
   ASTROCLK Astronomical Clock and Celestial Tracking Program        Page 4


        way to do this is simply to run ASTROCLK and observe the 
        displayed local time compared to an accurate clock or watch. 
        Second, if you temporarily leave ASTROCLK using Function Key F9, 
        note the time when you return to ASTROCLK and, if the time is in 
        error, make a note of what programs or operations in your system 
        affect the accuracy of the software clock. In either case, reset 
        your software clock from time to time if necessary or, if your 
        computer has a hardware clock, re-read your hardware clock to 
        take advantage of its superior accuracy. For many computers, 
        ASTROCLK can do this using Function Key ALT-F3.
             Using this more or less accurate time standard, ASTROCLK 
        displays the current Local Time and Local Date, the Local Mean 
        Sidereal Time ("star time"), and the Local Mean Solar Time 
        (referred to the local longitude). Also shown are: Coordinated 
        Universal Time (UTC) which, for years 1925 and later and to the 
        accuracy used here, is the same as Greenwich Mean Time (GMT); the 
        UTC Date at the Prime Meridian (Greenwich, longitude 0 degrees); 
        Greenwich Mean Sidereal Time; and, the local time zone relative 
        to UTC. All times are in 24-hour notation and local time is Local 
        Standard Time or Local Daylight Time, depending upon the setting 
        of the DAYLIGHT FLAG. If your time zone is offset from the 
        computed local time zone, see also the section SETTING PROGRAM 
        OPTIONS. Note that dates are shown as DD-MM-YYYY (European style, 
        day-month-year) and that because of the time span covered the 
        full 4-digit year is required. Any one of the times may be 
        displayed in a main window with extra large digits for easy 
        visibility.
             Precision Time and Data Displays are available which show a 
        variety of common time standards to a precision of 0.0001 seconds 
        along with other astronomical information. The display is updated 
        each second -- provided the computer can make the necessary 
        calculations in that time. If the clocks are stopped, the user 
        may enter any desired time and date and view the calculated 
        values for all of these items to a high degree of accuracy. The 
        values have been carefully checked against the Astronomical 
        Almanac, prepared each year jointly by the U. S. Naval 
        Observatory (USNO) and the Royal Greenwich Observatory, and the 
        USNO Floppy Almanac and are believed accurate to within plus or 
        minus 0.01 seconds or better; note that the displayed precision 
        is 0.0001 seconds.
             Initially, the program assumes the geographical location of 
        Rancho Palos Verdes, California, near Los Angeles. However, an 
        auxiliary file contains the names and locations of a number of 
        American and Canadian cities which can quickly be read by 
        ASTROCLK. The file may easily be edited to include your favorite 
        locations and their coordinates. If you change the local 
        coordinates, ASTROCLK saves them in a special file, ASTROCLK.INI, 
        and the new place name and coordinates will be automatically 
        loaded when the program is next started.
             A tracking feature is included which allows the user to 
        continuously display the celestial and horizon (observer) 
        coordinates for the pole star, Polaris, and the 57 stars 
        designated by the U. S. Naval Observatory (USNO) as "Standard 
        Navigational Stars". Data for these stars are preset in the 
        program and are for Epoch J2000.0, the current standard epoch for 
   ASTROCLK Astronomical Clock and Celestial Tracking Program        Page 5


        celestial coordinates. The list of these standard stars is from 
        USNO, and the actual coordinates have been taken from the USNO 
        Floppy Almanac 1988. The data for proper motion is also included 
        for the correct calculation of precession.
             Alternatively, the user may search an external star catalog 
        for a desired star using the catalog number or any of several 
        star names. The supplied catalog, ASTROCLK.CAT, contains 1645 
        stars and objects whose coordinates have been calculated by USNO 
        and which are also for Epoch J2000.0. Finally, the user may 
        manually enter the celestial coordinates (right ascension and 
        declination) for a star, planet, or other object. Once the 
        celestial coordinates have been selected or entered, ASTROCLK 
        continually displays the local (or "observer horizon") 
        coordinates as well as the Sidereal Hour Angle (SHA, preferred by 
        navigators), computed once per second. The program also displays 
        coordinates adjusted for atmospheric refraction, important as an 
        object approaches the horizon. Using a small portable computer, 
        the would-be stargazer may take the program into the field and 
        use it to locate and track the desired object.
             The user may also enter the local horizon coordinates, 
        Altitude and Azimuth, for a bright star and ask ASTROCLK to 
        select the USNO Standard Navigational Star which is closest to 
        the position entered at that time. It will also find Polaris if 
        the coordinates are close enough, but the algorithm for star 
        selection is less accurate near the poles. The same process may 
        be used with the external star catalog. So the program works both 
        ways: it can tell you where to look for a selected star or, if 
        you tell it where you see a star, it can tell you which star you 
        are probably looking at.
             By stopping the real time clock and entering a date and time 
        of choice, the user may also determine the position of a 
        celestial object at any time in the past or future. However, 
        since some formulae and star coordinates assume the present 
        epoch, J2000.0 usually, the accuracy of positions calculated may 
        decrease for epochs distant from modern times. A simulation mode 
        may be used to view data in simulated real time at any preset 
        time and date.
             When desired, ASTROCLK will perform the calculations 
        required to predict the coordinates of the major planets or, 
        using an external catalog, of minor planets, comets, and 
        asteroids. ASTROCLK can display a variety of information for the 
        planets, and will provide tracking data as with the USNO Standard 
        Navigation Stars. The accuracy of the planetary positions has not 
        been checked over longer time spans. See the sections PLANETARY 
        DATA DISPLAYS and MINOR PLANET SELECTION for further discussion.
             Inspired by several long sea journeys, ASTROCLK can perform 
        a number of navigational functions, including dead reckoning and 
        celestial navigation. While the accuracy is not quite as high as 
        can be achieved with the Nautical Almanac (and a lot of tiresome 
        calculations) or by sophisticated satellite navigation systems, 
        it is sufficient to get in the right neighborhood. With "perfect" 
        star sights, the accuracy is approximately 0.25 nautical miles.
             ASTROCLK includes a perpetual calendar which will display 
        any month of any year from -4713 B.C. into the future. The 
        default calendar algorithms follow the Julian Calendar from -4713 
   ASTROCLK Astronomical Clock and Celestial Tracking Program        Page 6


        B.C. until October 4, 1582 after which the Gregorian Calendar is 
        used. This follows civil usage in catholic countries as well as 
        astronomical convention, but will not correspond to the date 
        convention used in countries which did not adopt the Gregorian 
        Calendar in October of 1582. Great Britain and its colonies 
        (including what is now the United States), for example, did not 
        adopt the Gregorian Calendar until September 2, 1752. Dates prior 
        to the introduction of the Julian Calendar in 46 A.D. are in 
        accordance with the Julian Proleptic Calendar (the Julian 
        Calendar extended backwards in time from 46 A.D.) and are 
        therefore more or less a figment of the program's imagination; 
        the dates computed are consistent with that calendar (and 
        astronomical convention) but bear no relation to any calendar in 
        actual use at the time. A program option is available to choose 
        between the strict Julian calendar and either the 1582 or the 
        1752 adoption of the Gregorian calendar. An additional date 
        display is also available which shows several styles of Julian 
        Date, the local date, the current day of the year, and the day of 
        the week.
             ASTROCLK is presently being used at several observatories 
        for both time and tracking displays. Beginning with Version 8903, 
        the display may be set to the RED mode so that all displays are 
        presented in red; the monitor intensity may then be adjusted for 
        best comfort and protection of night vision. A GREEN mode is also 
        available which may reduce eye fatigue during periods of extended 
        use.
   ASTROCLK Astronomical Clock and Celestial Tracking Program        Page 7



        HARDWARE REQUIREMENTS

             ASTROCLK was designed for and is best operated using a color 
        adapter and color monitor, CGA/EGA/VGA. The program can be forced 
        to emulate monochrome output on color video adapters with the 
        "/M" command line option. Limited tests on a monochrome system 
        (true monochrome adapter and display, as opposed to a system 
        using a monochrome display on a color-compatible adapter), have 
        been successful when used with the "/M" command line option. The 
        program has so far been tested on the following systems:

                  ALR 20386DT Computer
                  VGA Video Graphics Adapter (Paradise VGA Plus)
                  VGA High Resolution Color Display (Zenith ZCM-1490)
                  80387 math coprocessor

                  Zenith Z-386 Computer
                  VGA Video Graphics Adapter (Zenith Z-449)
                  VGA High Resolution Color Display (Zenith ZCM-1490)
                  80287 math coprocessor

                  Zenith Z-248 (IBM PC-AT compatible)
                  VGA Video Graphics Adapter (Paradise VGA Professional)
                  VGA High Resolution Color Display (Zenith ZCM-1490)
                  80287 math coprocessor

                  Zenith Z-248 (IBM PC-AT compatible)
                  EGA Enhanced Graphics Adapter (Quadram QuadEGA and 
                       Zenith Z-449)
                  ECD Enhanced Color Display (Princeton HX-12E)
                  80287 math coprocessor

                  Zenith Z-248 (IBM PC-AT compatible)
                  VGA Video Graphics Aray (Paradise VGA Professional)
                  Monochrome Display (Zenith ZVM-1240)
                  No math coprocessor

                  Zenith Z-181 and Z-183 Laptop Computers
                  Internal CGA Color Graphics Adapter
                  Internal Twisted-Crystal Display
                  No math coprocessor

                  Zenith Z-151 (IBM PC-XT compatible)
                  Standard CGA/Composite Color Graphics Adapter 
                  Monochrome Monitor (Zenith ZVM-1230A) 
                  Color Monitor (Mitsubishi CS-2061R)
                  8087 math coprocessor

                  Zenith Z-148 (IBM PC-XT compatible)
                  Internal CGA Color Graphics Adapter 
                  RGBI Color Monitor
                  No math coprocessor

             Several users have also reported successful operation on 
   ASTROCLK Astronomical Clock and Celestial Tracking Program        Page 8


        other systems including an IBM PS/2 Model 80 and a Compaq Model 
        386/20. The program has also been tested on various "IBM-clone" 
        systems with numerous variations including CGA/EGA/VGA Graphics 
        Adapters and Hercules Graphics Adapters (HGC). The only problem 
        encountered was with a 101-key keyboard emulator (supplied by 
        Microsoft!) which caused the system to hang when ASTROCLK was 
        executed; a reboot was required to resume operation. When the 
        emulator program was removed, ASTROCLK executed without 
        difficulty.
             Several ASTROCLK functions use the QuickBASIC SHELL command 
        to execute DOS commands directly or to return the user to a 
        secondary command processor (Function Key F9). All of my systems 
        use MS-DOS Version 3.1 or higher but I have read reports that 
        the QuickBASIC SHELL does not operate correctly for versions of 
        MS-DOS or PC-DOS of 3.0 or lower. I recommend that you upgrade to 
        Version 3.2 or higher for better system performance in general 
        and to avoid problems with the SHELL command in particular.
             ASTROCLK supports the EGA 43-line mode to a limited extent: 
        if the system is in that mode at program startup, it will return 
        to that mode upon final exit. I'm rather fond of the EGA's 35-
        line mode and often use it in preference to either 25- or 43-line 
        modes. Unfortunately for me, QuickBASIC (any version) refuses to 
        recognize the 35-line mode on entry and returns the system to the 
        25-line mode upon exit. Regardless of the screen mode detected at 
        the start of execution, ASTROCLK always sets the system to 80 
        columns and 25 lines for maximum compatibility and ease of 
        viewing.
             The "/M" command line option (see PROGRAM OPERATION, below) 
        is recommended for systems equipped with a monochrome display 
        adapter and monochrome monitor. It also forces monochrome display 
        on computers which have CGA-compatible video adapters but 
        simulate colors with shades of gray or varying intensities of a 
        single color, such as the Zenith Z-181 and Z-183; these computers 
        otherwise require some adjusting to see the shades of blue, 
        especially bright white on green background (used for LOCAL 
        COORDINATES and HELP screens). The green monochrome monitor on my 
        Z-151, on the other hand, rendered all colors visible. Results 
        will obviously vary from system to system. Limited tests have 
        been performed on systems equipped with a monochrome video 
        adapter using the "/M" command line option and the program 
        performed properly.
             The performance of different computers varies considerably, 
        the single most important factor being the presence or absence of 
        a math coprocessor. Program ASTROCLK uses the double precision 
        floating point format for almost all significant calculations, 
        and the added performance of the coprocessor is significant. 
        Without it, even an AT-class computer has perceptible delays in 
        the Precision Time and Data Displays; with it, an old PC-class 
        computer easily completes the same tasks within one second. To 
        measure the performance under these conditions, a special version 
        of program ASTROCLK was prepared to time the nutation and 
        obliquity of the ecliptic calculations required for the 
        computation of Apparent Sidereal Time. The following table shows 
        the results of the tests on several different computer 
        configurations ranging from a PC/AT-compatible to my oldest 
   ASTROCLK Astronomical Clock and Celestial Tracking Program        Page 9


        machine, a PC/XT-compatible. For comparison, the Norton Utilities 
        System Information Computing Index (SI) is shown. Computation 
        time only is measured for a single iteration of the calculations 
        (8825) and for the average of ten interations (8826A). Unless 
        otherwise noted: the compiled version of ASTROCLK was used; all 
        computers were running MS-DOS Version 3.1 or higher; all computer 
        models are Zenith part numbers; and, all times are in seconds and 
        are typical except clock speed is in MHz. The math coprocessor is 
        not the only factor in execution speed; significant software 
        improvements were made in Version 8826A as compared to Version 
        8825. The times for both versions are shown for comparison. (Not 
        all system configurations were available for testing Version 
        8826A.)

                     CPU/COPROCESSOR PERFORMANCE COMPARISONS
                     ---------------------------------------

                                                   8825    8826A
             MODEL    CLOCK    CPU       COPRO     TIME    TIME**   SI
             ---------------------------------------------------------
             Z-386   16.00     80386     -----     0.88    0.07
             Z-248    8.00     80286     80287     0.38*           9.0
             Z-248    8.00     80286     80287     0.27    0.015   9.0
             Z-248    8.00     80286     -----     1.65            9.0
             Z-183    4.77     80C88     -----     9.35    0.87    1.0
             Z-183    8.00     80C88     -----     6.59    0.60    1.6
             Z-151    4.77     V-20      8087      0.60    0.03    1.8
             Z-148    4.77     8088      -----     9.35    0.85    1.0
             Z-148    8.00     8088      -----     5.48    0.51    1.7

             *  QuickBASIC interpretive mode
             ** Average of 10 iterations of calculations

             All machines performed "normal" calculations without undue 
        delay. The various clock displays were updated every second and 
        only in the Target Tracking Display, Precision Time and Data 
        Displays, and the Planetary Data Displays (modes 0, 8 and 9) were 
        computational times very noticeable; slower machines, especially 
        any machine without a math coprocessor, required from 2 to 5 
        seconds to update the calculations depending upon the mode. 
        Planetary position calculations, being the most complex, require 
        the most computational time and involve the greatest delays.
             I have not tested the minimum memory requirements for 
        ASTROCLK. All of my systems are equipped with 640K. As of Version 
        8907, the program requires more than 200K bytes of memory and 
        probably WILL NOT execute in a minimum 256K system. Since 
        ASTROCLK can invoke QuickBASIC's SHELL command to return you 
        temporarily to DOS with ASTROCLK still in memory, I recommend the 
        use of 640K memory. However, even with 640K of memory, the fact 
        that ASTROCLK is resident means that programs which require a 
        great deal of memory may fail to execute properly under the 
        shell. These programs must be executed outside ASTROCLK.
             Comments and test results from other system configurations 
        are welcome. Note that future versions of ASTROCLK may require 
        additional memory and/or disk space.
   ASTROCLK Astronomical Clock and Celestial Tracking Program        Page 10



        PROGRAM OPERATION

             This section describes the operation of program ASTROCLK, 
        including required files, starting the program, and initial 
        operations.


        Required ASTROCLK Files

             Program ASTROCLK is normally distributed in archived form 
        and includes the following files:

                  ASTROCLK.EXE        Executable ASTROCLK program
                  ASTROHLP.EXE        Executable ASTROHLP program

                  ASTROCLK.BAS        Main ASTROCLK source for QB4
                  ASTROCLK.CAT        Data file of additional stars
                  ASTROCLK.CTY        Data file of cities/locations
                  ASTROCLK.DC1        ASTROCLK Documentation, Part I
                  ASTROCLK.DC2        ASTROCLK Documentation, Part II
                  ASTROCLK.HST        Revision history for ASTROCLK
                  ASTROCLK.INI *      Data file for initialization
                  ASTROCLK.MAK        Source module list for QB4
                  ASTROCLK.MPC        Minor Planet Catalog
                  ASTROCLK.PIF        PIF file for Microsoft WINDOWS
                  ASTROFNT.COM        EGA Soft Font (EXPERIMENTAL)
                  ASTROHLP.BAS        Program source for ASTROHLP, QB4
                  ASTROSB1.BAS        SUB/PROCEDURE source for QB4, 1/3
                  ASTROSB2.BAS        SUB/PROCEDURE source for QB4, 2/3
                  ASTROSB3.BAS        SUB/PROCEDURE source for QB4, 3/3
                  MESSIER.CAT         Data file of Messier objects only
                  READ.ME      *      Latest information/changes
                  USCITIES.CTY        718 U. S. city coordinates

                  *  May not be present in archived files

             Program ASTROCLK if often distributed via bulletin board 
        systems and on disk as three compressed files. A complete version 
        should contain ALL of the listed files except as noted. Depending 
        upon the source, different file compression programs may be 
        required to unpack the files; the required program is usually 
        indicated by the filetype of the archived files.
             Only the files ASTROCLK.EXE and ASTROHLP.EXE are required 
        for operation of the program. If necessary, file ASTROHLP.EXE may 
        be omitted but the on-screen help functions will not operate and 
        no warning message will be given.
             File ASTROCLK.CTY adds the capability to read the location 
        of various U. S. and Canadian cities; a warning message is 
        displayed if it is not present and a search of the file is 
        attempted. File ASTROCLK.CAT contains data for 1645 stars and 
        galaxies which may be requested by name or number; a warning 
        message is displayed if the file is not present and a catalog 
        search is requested. File ASTROCLK.INI is not normally included; 
        it is quite small and will be created automatically. File 
   ASTROCLK Astronomical Clock and Celestial Tracking Program        Page 11


        ASTROCLK.PIF allows the program to be run under Microsoft WINDOWS 
        if sufficient memory is available; it has been tested with 
        Version 2.03. File READ.ME contains recent information or changes 
        not described in this file and may or may not be included.
             An additional catalog file, MESSIER.CAT, contains data for 
        the 109 Messier objects which has been extracted from file 
        ASTROCLK.CAT, for convenience in locating these objects. An 
        additional city file, USCITIES.CTY contains coordinates for 718 
        U. S. cities to higher accuracy than file ASTROCLK.CTY.
             Beginning with Version 8908, ASTROCLK can also process and 
        track minor planets, comets, and asteroids. File ASTROCLK.MPC is 
        an external binary catalog containing the first 250 minor planets 
        which may be selected by Minor Planet Number or Name. The binary 
        catalog has been prepared with my program MPCAT, developed for 
        this purpose, using data compiled by E. G. Bowell of the Lowell 
        Observatory and provided by Ed Tedesco of the Jet Propulsion 
        Laboratory. The full minor planet catalog, EPHEM891.MPC with 
        3,774 minor planets, comets, and asteroids, is available 
        separately from my bulletin board system. New updated minor 
        planet catalogs are released at approximately six month 
        intervals. These versions of the minor planet data have been 
        converted into the binary format expected by ASTROCLK using 
        program MPCAT; as with program ASTROCLK, the current version of 
        MPCAT and the source are always available from my bulletin board 
        system (BBS). See the section A BRIEF EDITORIAL for more 
        information on the BBS.
             As an experiment for EGA users, file ASTROFNT.COM provides 
        an alternate screen font. The screen typeface is changed from its 
        normal appearance to a cleaner typeface resembling Helvetica. To 
        use this screen font, enter "ASTROFNT" prior to executing program 
        ASTROCLK (the cursor may disappear but don't worry!) or press the 
        letter "E" during normal operation. CAUTION: Use of ASTROFNT with 
        other display adapters may produce unpredictable results!
             ASTROCLK is written and compiled using Microsoft QuickBASIC, 
        Version 4.50. Source files ASTROCLK.BAS, ASTROSB1.BAS, 
        ASTROSB2.BAS, and ASTROSB3.BAS are all required for use with the 
        compiler. In addition, ASTROCLK.MAK is required for use in the 
        interpreter mode. Although I normally compile and link from 
        within QuickBASIC, the following batch file may be used to 
        compile and link ASTROCLK to produce a stand-alone .EXE file (all 
        files assumed in the current drive and directory):

             bc astroclk/e/x/o/t/c:512;
             bc astrosb1/o/t/c:512;
             bc astrosb2/o/t/c:512;
             bc astrosb3/o/t/c:512;
             link /ex astroclk+astrosb1+astrosb2+astrosb3,astroclk.exe;

        Note that the compile and link commands may be particular to the 
        versions of BC and LINK being used, Version 4.50 and Version 3.69 
        respectively in this case. See A BRIEF EDITORIAL near the end of 
        this document for information on how to obtain the most recent 
        version of all ASTROCLK files.
             Users who require minimum size run files because of memory 
        constraints may choose to compile and link ASTROCLK to use 
   ASTROCLK Astronomical Clock and Celestial Tracking Program        Page 12


        Microsoft's runtime module, BRUN45.EXE, instead of generating a 
        standalone program. Approximately 40K less RAM memory is required 
        for ASTROCLK in this configuration. However, this configuration 
        is less flexible with respect to starting directory: BRUN45.EXE 
        must be in the same directory as ASTROCLK.EXE, and ASTROCLK must 
        be run from that directory. Batch files which work correctly with 
        the standalone version may have to be modified.
             Beginning with Version 8933, the help functions for ASTROCLK 
        were removed to a separate program, ASTROHLP.EXE, automatically 
        executed by Function Key F1. The source file for help is 
        ASTROHLP.BAS. This change reduced the size of the main ASTROCLK 
        program by 10K bytes and reduced the RAM memory requirements by 
        about the same amount, but subsequent versions have more than 
        used up the memory again.


        Starting Program ASTROCLK

             To start ASTROCLK, first verify that your computer is set to 
        the correct local time and date using the TIME and DATE commands, 
        then enter one of the following commands at the DOS prompt:

                  ASTROCLK       [for all COLOR monitors]

                  ASTROCLK /M    [for MONOCHROME monitors]

                  ASTROCLK /R    [to force RED on color monitors]

                  ASTROCLK /G    [to force GREEN on color monitors]

        followed by RETURN (or ENTER, which I will call RETURN) and the 
        program will begin execution. The descriptions and examples in 
        this documentation assume you are using a color monitor; if you 
        are using a monochrome monitor, ignore all references to colors. 
        However, all users should note that negative years, described as 
        RED in this documentation, will BLINK in the program's date 
        windows when the "/M" option is used or when either of the single 
        color program modes is set; the UTC Julian Date window, of 
        course, will show the correct number for all dates.
             Using one of the command line color options forces the 
        program to that color mode immediately and overrides any prior 
        color mode. When a color option is NOT used, ASTROCLK will 
        initially display its signon screen in full color (for color 
        monitors); using the "/R" or "/G" color option will use the 
        selected color for the signon screen as well as all subsequent 
        operations. This is particularly useful with the RED option to 
        protect night vision when alternating between ASTROCLK and other 
        programs. ASTROCLK may also be switched between the monochrome, 
        color, red, and green modes during execution using Function Key 
        ALT-F10. See the section SETTING PROGRAM OPTIONS for further 
        information.
             As initially configured, ASTROCLK assumes that the all data 
        files are in the current drive and directory. If this is not the 
        case, you may include the drive and path for the various ASTROCLK 
        data files using the following command pattern (note space after 
   ASTROCLK Astronomical Clock and Celestial Tracking Program        Page 13


        ASTROCLK):

                  ASTROCLK [drive:][\path][coloroption]

        "drive:" must be a single letter followed by a colon and must 
        correspond to a valid drive. If no path is included, ASTROCLK 
        assumes the current directory on the specified drive or, if no 
        drive is included, on the current drive. If the path is included, 
        it must begin with the backslash, "\", and the path must exist. 
        See your DOS manual for an explanation of paths and directories. 
             If present, the color option must follow the drive and/or 
        path; only ONE of the color options /M, /R, or /G may be used to 
        force MONOCHROME, RED or GREEN respectively. Using a color option 
        will override any prior color setting saved in file ASTROCLK.INI. 
        If no color option is included on the command line, ASTROCLK will 
        start in full color, then read the file ASTROCLK.INI (if present) 
        and set the color to the mode last used.
             For example, if all data files are on disk drive B: in 
        subdirectory ASTROCLK and you want to force monochrome display, 
        the following command should be used:

                  ASTROCLK B:\ASTROCLK/M

                              ********************
                              *  IMPORTANT NOTE  *
                              ********************

             Once ASTROCLK has been executed the first time, the drive 
        and path information are saved in the program initialization 
        file ASTROCLK.INI. Thereafter, ASTROCLK uses the information 
        in ASTROCLK.INI and overrides any drive or path specification
        entered on the command line. However, the command line color 
        options (/M, /R, or /G), if present, will take precedence over 
        the previous color saved in the file. Use Function Key ALT-F10 to 
        change the drive and/or subdirectory from within ASTROCLK, or 
        delete file ASTROCLK.INI at the DOS prompt to start over. See the 
        section SETTING PROGRAM OPTIONS for additional information.

                                    * * * * *


        Running Program ASTROCLK

             When ASTROCLK begins, a title screen will appear and the 
        program will perform various initialization tasks. After a few 
        seconds ASTROCLK will display the Local Standard Time (or 
        Daylight Time if it has previously been set using the DAYLIGHT 
        FLAG entry with Function Key ALT-F10) in the main display window 
        and all clocks will be running. For time zones in the United 
        States, the correct zone name will be displayed.
             The program reads your DOS software clock for the current 
        time and date; set your system clock accurately before you run 
        ASTROCLK using your hardware clock if your computer has one or 
        using the TIME and DATE commands if not. If your version of 
        MS-DOS includes the program RTCLOCK (supplied with Zenith 80286, 
   ASTROCLK Astronomical Clock and Celestial Tracking Program        Page 14


        80386, and laptop computers), you may use ALT-F3 to set the 
        system clock from the internal hardware clock. If the program to 
        read your hardware clock has a different name, create a batch 
        file named RTCLOCK.BAT which includes the required command(s), 
        make sure it can be located via the PATH command, and then you 
        may use ALT-F3 to update the software clock.
             For example, my Zenith Z-151 includes a special (non-Zenith) 
        hardware clock which requires a program called RDCLOCK to set the 
        software clock from the hardware clock. I reset the software 
        clock using the following command in a batch file called 
        RTCLOCK.BAT:

                  RDCLOCK >NUL

        This reads the hardware clock, sets the software clock, and sends 
        its screen output to the "bit bucket" (throws it away to a 
        special DOS device called "NUL") so that it does not disturb my 
        ASTROCLK display.
             I have also noticed that for some systems the software clock 
        is not set properly when the system boots but is slow by some 
        five or ten seconds. This may be a peculiarity of the Zenith MS-
        DOS 3.2x software being used on the system in question, but 
        apparently the computer reads the hardware clock at some point 
        during the boot process, then does something which suspends the 
        clock before it turns the system over to me. I have solved the 
        problem by inserting the RTCLOCK command near the end of my 
        AUTOEXEC.BAT file. Now the software clock is set again after all 
        of the odds and ends have been gotten out of the way.
             If you do not have a program which reads your hardware clock, 
        or if you do not have a hardware clock, you can exit temporarily 
        back to DOS using Function Key F9 to set or reset the time and/or 
        date with the DOS TIME and DATE commands. Then enter EXIT to 
        return to ASTROCLK. 
             It is also possible to "fool" ASTROCLK by setting the DOS 
        system clock to any desired date and time. However, because of an 
        internal DOS software limitation, the DOS clock may only be set 
        for years from 1980 through 2199; in general, I recommend that 
        you use ASTROCLK's SIMULATION mode of operation for non-current 
        dates.

                                  *************
                                  *  CAUTION  *
                                  *************

             Beginning with DOS Version 3.3, the DOS DATE and TIME 
             commands may set BOTH the software AND the hardware 
             clocks for most AT-class and 386-class computers as 
             well as some others. Therefore, do NOT use the DOS DATE 
             and TIME commands with DOS Version 3.3 and higher if 
             you wish to preserve the setting of the hardware clock.

             The program automatically presets the celestial coordinates 
        for the star POLARIS (Alpha Ursae Minoris), the first and 
        brightest star of the constellation Ursa Minor (Little Bear). 
        POLARIS is commonly referred to as the pole star because of its 
   ASTROCLK Astronomical Clock and Celestial Tracking Program        Page 15


        close proximity to the celestial (and geographical) North Pole. 
        As a result, it has long been used for navigation and the 
        alignment of astronomical instruments. More recently, it is often 
        used to align satellite dishes.
             Since I don't know where you live, the program starts out 
        with the geographical coordinates for Rancho Palos Verdes, 
        California, near Los Angeles. These coordinates are displayed in 
        the lower left portion of the screen. However, in order to use 
        the sidereal time and celestial tracking features for your own 
        location, you need to know your local longitude (West is 
        negative) and latitude (South is negative).
             Goode's World Atlas, 17th Edition, (see BIBLIOGRAPHY) is an 
        ideal reference for this purpose; the Index contains some 30,000 
        cities and other locations worldwide along with their 
        geographical coordinates to a precision of one minute. While I 
        cannot vouch for the accuracy of the data, Goode's is the only 
        atlas I know with this information, a new feature with the 17th 
        Edition. With a little care, your local coordinates can also be 
        interpolated to an accuracy of about ten minutes of arc using a 
        good, detailed road map provided the map includes the fiducial 
        marks for longitude and latitude.
             Use Function Key F6 to input your local coordinates and 
        local place name; see also the section SETTING LOCAL COORDINATES 
        for a listing of the coordinates of selected cities in the United 
        States and Canada. If your location is near one of the these 
        cities, the coordinates can be read directly from file 
        ASTROCLK.CTY. The file is in standard ASCII code, and may be 
        edited to include additional cities and locations using any 
        editor provided the proper format is observed; WordStar and other 
        word processor users, use the ASCII or "Non-document" mode.
             Both geographical and celestial data can be entered (and 
        displayed) in several different formats. Celestial coordinates 
        may be entered or displayed as degrees plus decimal degrees, 
        degrees plus minutes and decimal minutes, or degrees plus minutes 
        plus seconds and decimal seconds. All of these methods are 
        acceptable to ASTROCLK although the separator varies (colon or 
        comma for times, comma for degrees and dates).

                                    * * * * *

                           EUROPEAN USERS PLEASE NOTE

             Both in this documentation and in program ASTROCLK itself, 
        the period (point, ".") is used for the decimal point to separate 
        the integer and fractional parts of a number rather than the 
        comma (virgule, ",") as is the practice in many European 
        countries. This usage is sufficiently deeply buried in the 
        software that it is impractical to make it dynamically 
        configurable. American users have to contend with dates entered 
        in the European style (DD,MM,YYYY), so I've managed to make 
        things a little inconvenient for everyone!

             Egalement ici dans cette texte et en le programme ASTROCLK, 
        le point (".") plutot que la virgule (",") est utilize pour 
        separer les deux parties d'un nombre, le nombre entier et le 
   ASTROCLK Astronomical Clock and Celestial Tracking Program        Page 16


        fragment. C'est usage commun ici aux Etats Unis. Domage, mais il 
        faut que les Americains utilizent les dats comme les Europeennes 
        (jour, mois, ans). C'est dificile pour tous le monde! [Traduction 
        grace a Dictionnaire Larousse, moins les accents.]

                                    * * * * *

             When ASTROCLK first starts, the current Local Standard Time 
        is displayed in the main window in large numerals. The number 
        keys 0 through 9 (on the top row of the keyboard) and several 
        other keys select the display mode for the main window: 

             1    LST/LDT   Local Standard/Daylight Time
             2    UTC       Coordinated Universal Time
             3    LMST      Local Mean Sidereal Time
             4    GMST      Greenwich Mean Sidereal Time
             5    TDT/ET    Terrestrial Dynamical/Ephemeris Time
             6              Perpetual Calendar
             7              Additional Date Information
             8              Precision Time and Data Displays
             9              Planetary Data Displays
             0              Celestial Tracking Display

             T              Interval Timer Display
             A              Alarm Countdown Display [if Alarm is set]

             Function Key F1 gives quick help for the function keys, but 
        should not be considered a substitute for this documentation.
             Using Function Key F7, the information displayed on the 
        Target Tracking Display at the left of the screen can be switched 
        between several formats including whole units (hours or degrees 
        as the case may be) plus decimal units, or a more conventional 
        display (hours, minutes, seconds or degrees, minutes, seconds). 
        Pressing ALT-F7 will change the Target Tracking Display 
        coordinates from Right Ascension (hours) to Sidereal Hour Angle 
        (degrees) and Hour Angle (hours) to Greenwich Hour Angle 
        (degrees), forms preferred by navigators.
             With the exception of the Julian Date (which is displayed to 
        six decimal places), the running clocks are displayed to the 
        nearest second. Other data are displayed to 0.000001 degrees or 
        hours, 0.0001 minutes of time or arc, or to 0.01 seconds of time 
        or arc, depending upon the display format selected with Function 
        Key F7. The Precision Time Display (Display Mode 8) gives various 
        time information to a precision (and approximate accuracy) of 
        0.0001 seconds. Most internal calculations are made in 
        QuickBASIC's DOUBLE PRECISION data format to yield maximum 
        accuracy and precision, but not all data are necessarily accurate 
        to the precision displayed. See the section PRECISION AND 
        ACCURACY TESTS for additional information.
             When the clocks are ON, ASTROCLK checks the system time and 
        attempts to begin a new set of calculations each second. Since 
        these calculations tend to be complex and time consuming, some 
        slower computers may not finish the task within the allotted 
        time. My Zenith Z-183 laptop, running at 8 MHz but with no math 
        coprocessor, skips every third or fourth second when operating in 
   ASTROCLK Astronomical Clock and Celestial Tracking Program        Page 17


        the Target Tracking Mode and the Precision Time and Data 
        Displays. This does not affect the accuracy of the displayed 
        data, only the frequency with which it is updated. For 
        comparison, my old Zenith Z-151 running at 4.77 MHz but with an 
        8087 math coprocessor, manages to keep up just fine. Regardless 
        of the computer type, a math coprocessor will substantially 
        decrease computation times. See the performance comparisons in 
        the section HARDWARE REQUIREMENTS. Version 4.50 of Microsoft's 
        QuickBASIC, the programming language used for ASTROCLK, 
        automatically senses the presence of a math coprocessor and uses 
        it if it is available.
             To exit ASTROCLK, press ESC and you will return to the DOS 
        prompt. ASTROCLK always rewrites the file ASTROCLK.INI prior to 
        exit in order to reflect the current coordinates, flags, display 
        modes and other information. Each time ASTROCLK is started it 
        checks for file ASTROCLK.INI and reads its contents if present. 
        If you change the coordinates, the new coordinates will be used 
        the next time you run ASTROCLK.
   ASTROCLK Astronomical Clock and Celestial Tracking Program        Page 18



        FUNCTION KEYS AND HELP

             Function Key F1 invokes a HELP function which displays the 
        operation performed by the ten Function Keys, F1 through F10 (as 
        well as several ALT or SHIFT plus Function Key combinations). 
        While the operations are generally self explanatory, positioning 
        the flashing red pointer at the desired operation (F1 through 
        F10) with the Up or Down arrow keys and pressing RETURN will 
        display additional information. Pressing the desired Function Key 
        directly will also display the supplementary information for that 
        Function Key. Press RETURN (or any other key) to return to the 
        main HELP menu. Press the SPACE BAR to exit the main HELP menu 
        and return to normal program operation.
             All of the displayed clocks are stopped while using HELP and 
        the message "Clocks OFF" will be displayed in flashing red at the 
        upper right of the screen. If the clocks were on when HELP was 
        requested, the clocks will resume normal or simulated operation 
        when you leave HELP and the message "Clocks ON" or "SIMULATION" 
        will again be displayed in green or yellow respectively at the 
        upper right of the screen. If the clocks were off when HELP was 
        requested, they will remain off when you leave HELP.
             The following operations are available with the ten Function 
        Keys, F1 through F10:

             F1   Display HELP screens. Display program name, version, 
                  and date if pressed again when the main HELP screen is 
                  visible.

             F2   Display Target Object EPHEMERIS. Before pressing F2, 
                  set the desired start time using F3, then select the 
                  desired target object using F5. Press F2 and enter the 
                  desired step interval and the number of intervals. The 
                  ephemeris information is displayed on the screen. When 
                  done or if more than 20 intervals are requested, the 
                  display will pause; press any key to contiue. Use the 
                  SHIFT-PrtSc to obtain a printed copy of the ephemeris.

             F3   Set LOCAL/UT TIME and/or LOCAL/UT DATE. The on-screen 
                  clocks are running when the time and date are set to 
                  the system clock or when the SIMULATION mode has been 
                  enabled with ALT-F4. (If the clocks are stopped, press 
                  F4 to restart the clocks.) When entering time or date, 
                  press RETURN to skip an entry and leave that item 
                  unchanged. F3 automatically cancels the SIMULATION 
                  mode.

                  LOCAL/UT/TDT TIME: Enter as Hours, Minutes, Seconds 
                  using 24 hour notation; use either the comma or the 
                  colon as separator. Decimal fractions are permitted for 
                  any item. Add the letter "U" at the end of the entry to 
                  enter UT TIME instead of local time; add the letter "T" 
                  or "E" at the end of the entry to enter TDT/ET TIME 
                  instead of local time.

   ASTROCLK Astronomical Clock and Celestial Tracking Program        Page 19


                  NOTE: Use ALT-F10 to set the DAYLIGHT FLAG and any 
                  required ZONE CORRECTION. See the section SETTING 
                  PROGRAM OPTIONS for an explanation.

                  LOCAL/UT DATE: Dates may be entered in a number of 
                  formats. For "standard" dates, enter the new date in 
                  the form DD,MM,YYYY. Note that the date is entered 
                  European style: Day, Month, Year and that the full 4-
                  digit year is required. Years B.C. (Julian proleptic 
                  calendar) are preceded by a minus sign (e.g. -4713). 
                  NOTE: There is no year 0000 in the day numbering 
                  algorithms used in ASTROCLK. Add the letter "U" 
                  following the year to enter UT DATE instead of local 
                  date. When UT TIME has been entered, UT DATE is 
                  automatically entered rather than LOCAL DATE. Dates may 
                  also be entered as the Julian or Sidereal date. Five 
                  styles of day numbers may be used, selected by the 
                  prefix used, as well as several other methods.

                  For a more complete explanation of time and date entry 
                  using F3, see the section SETTING LOCAL/UT/TDT TIME AND 
                  DATE.

                  Use ALT-F3 to read the hardware clock with program 
                  RTCLOCK from within ASTROCLK. (See PROGRAM OPERATION 
                  for details.)

                  Use SHIFT-F3 to set an ALARM TIME or to set the start 
                  time for the INTERVAL TIMER. The alarm may be set up to 
                  23 hours in advance. When set, a window appears at the 
                  lower right of the screen and displays the set alarm 
                  time and the time remaining in red. To set the start 
                  time for the Interval Timer, suffix the entered time 
                  with the letter T. To disable an already set alarm, 
                  press SHIFT-F3 then press RETURN. See also the section 
                  ALARM AND INTERVAL TIMER OPERATIONS for additional 
                  information.

             F4   Toggle Clocks ON or OFF. When clocks are ON, all time 
                  and date displays are referenced to the computer's 
                  internal software clock and any manually set local time 
                  or date is lost. When clocks are OFF, all times on the 
                  screen are frozen. The clocks are automatically turned 
                  OFF if either the local time or local date is set with 
                  Function Key F3. The message "Clocks ON" (green), 
                  "Clocks OFF" (flashing red), or "SIMULATION" (yellow) 
                  appears at the upper right of the screen to indicate 
                  the current clock status.

                  Use ALT-F4 to toggle simulated real time. First preset 
                  the desired time and date using Function Key F3, then 
                  press ALT-F4 to turn on the simulation. The word 
                  SIMULATION will appear in yellow at the upper right of 
                  the screen (in place of the Clocks ON/OFF message) when 
                  simulation is active. Press ALT-F4 again to disable 
   ASTROCLK Astronomical Clock and Celestial Tracking Program        Page 20


                  simulation. Function Key F3 also cancels the simulation 
                  mode. NOTE: Unlike the DOS clock, which may only be set 
                  for the period 1980 through 2099, the internal ASTROCLK 
                  simulation will operate for any time and date.

                  Function Key F4 may be used to start and stop the 
                  clocks in the simulation mode as usual. Function Keys 
                  F4 and ALT-F4 stop simulated time in different ways. 
                  When F4 is used to stop and start simulation, the 
                  simulated time will resume as if the clocks had not 
                  been stopped (the same as in the real time mode). Use 
                  of ALT-F4 disables the simulation and stops the clocks; 
                  pressing ALT-F4 again will restart simulation at the 
                  current indicated time. If F4 is pressed after ALT-F4 
                  has stopped simulation, normal real time operation will 
                  follow.

             F5   Set new star or celestial object TARGET COORDINATES 
                  using either the internal star database or an external 
                  star catalog. [NOTE: To set the target coordinates for 
                  a planet or to use the external Minor Planet Catalog, 
                  see the sections PLANETARY DATA DISPLAYS and MINOR 
                  PLANET SELECTION.]

                  A sub-menu is displayed offering the following function 
                  key selections:

                  F1   Enter the USNO Standard Navigational Star Number 
                       (1 through 57, or 0 for Polaris) or the desired 
                       Star Name to use the internally stored star data. 
                       When the name is entered, upper or lower case may 
                       be used and only sufficient letters to 
                       unambiguously identify the star name are required. 
                       Enter "Deneb " (with a trailing space) to 
                       distinguish that star from "Denebola".

                  F2   Search for nearest USNO Standard Navigational 
                       Star. Enter the local horizon coordinates in 
                       degrees: ALTITUDE (the angle from the true horizon 
                       up to the star) and AZIMUTH (the direction of the 
                       star in the sense North=0, East=90, South=180, and 
                       West=270). The program will search for the USNO 
                       star closest to the position specified and the 
                       data for that star will be displayed in the 
                       Tracking Window.

                  F3   Search EXTERNAL STAR CATALOG by star name, star 
                       identification, or catalog number. When the name 
                       is entered, upper or lower case may be used and 
                       only sufficient letters to unambiguously identify 
                       the star name are required. (Enter "Deneb ", with 
                       a trailing space, to distinguish that star from 
                       "Denebola".) Messier objects may be identified by 
                       common name ("ORION") or by Messier number ("M9"). 
                       If the program finds a matching entry in the 
   ASTROCLK Astronomical Clock and Celestial Tracking Program        Page 21


                       catalog, the data for that star will be displayed 
                       in the Tracking Window; if no match can be made, 
                       the data in the Tracking Window is left unchanged. 
                       Press SPACE BAR to cancel the catalog search in 
                       progress; the current data is left unchanged.

                  F4   Search EXTERNAL STAR CATALOG by Right Ascension 
                       and Declination. Enter the coordinates when
                       requested and the program will find the catalog 
                       stars closest to the position specified. Respond 
                       "Y" to display the 10 closest stars or "N" to only 
                       locate the closest star. Press RETURN to display 
                       the star in the Target Tracking Window. Press 
                       SPACE BAR to cancel the catalog search in 
                       progress; the current data is left unchanged.

                  F5   Search EXTERNAL STAR CATALOG for nearest star. 
                       Enter the local horizon coordinates in degrees: 
                       ALTITUDE (the angle from the true horizon up to 
                       the star) and AZIMUTH (the position of the star in 
                       the sense North=0, East=90, South=180, and 
                       West=270). The program will search the catalog for 
                       the stars closest to the position specified. Respond 
                       "Y" to display the 10 closest stars or "N" to only 
                       locate the closest star. Press RETURN to display 
                       the star in the Target Tracking Window. Press 
                       SPACE BAR to cancel the catalog search in 
                       progress; the current data is left unchanged.
    
                  F6   MANUAL DATA ENTRY. Enter the celestial 
                       coordinates, Right Ascension and Declination, the 
                       proper motion in Right Ascention and Declination 
                       per Julian century (in seconds of time or arc), 
                       and the object name as requested. If the proper 
                       motion parameters are not known, press RETURN to 
                       enter zero. If RETURN is pressed for the object 
                       name, the display will show "Manual Target Data". 
                       The data for the object will be displayed in the 
                       Tracking Window.

               RETURN  Cancel entry of Target Coordinates, leave current 
                       Target Coordinates unchanged, and resume normal 
                       program operation.

                  When searching using local horizon coordinates, 
                  altitude is measured in degrees up from the true 
                  horizon; 0 degrees is the horizon and 90 degrees is 
                  directly overhead. Don't forget to take into account 
                  hills or other obstructions that may obscure the true 
                  horizon. Azimuth is measured in degrees from true North 
                  in the sense NESW; thus, 0 degrees is North, 90 degrees 
                  is East, 180 degrees is South, and 270 degrees is West.

                  The star selection algorithm used in the various 
                  searches attempts to pick the Standard Navigational 
   ASTROCLK Astronomical Clock and Celestial Tracking Program        Page 22


                  Star or external catalog star which is closest (angular 
                  difference) to the coordinates you have entered. It may 
                  take a little practice before you can look at the night 
                  sky and estimate star positions accurately enough for 
                  the program to select the correct star. While the 
                  search is in progress, the message "SEARCHING ..." will 
                  appear at the upper right of the screen and the clocks 
                  will temporarily be stopped.

                  For an external catalog search, file ASTROCLK.CAT must 
                  be present. This catalog includes data for 1645 stars, 
                  Epoch J2000.0, extracted from USNO STAR1.CAT and USNO 
                  MESSIER.CAT. Stars may be requested by catalog number 
                  or by any of several names. See the section USING 
                  EXTERNAL STAR CATALOGS for additional information. 
                  While the search is in progress, the message "SEARCHING 
                  ..." will appear at the upper right of the screen and 
                  the clocks will temporarily be stopped.

                  NOTE: The supplied external star catalog is a large 
                  file, currently about 160Kb, and the search time on a 
                  floppy disk system is rather slow; the numbers 
                  appearing during the search indicate progress through 
                  the catalog in increments of 50.

                  For manual data entry, you must know the standard 
                  equatorial coordinates, Right Ascension and 
                  Declination, for the celestial object you wish to 
                  track. Star Atlases, astronomical magazines, and other 
                  publications usually give the coordinates for objects 
                  of interest. The input routine is very flexible and 
                  data may be entered in a number of formats. Observe the 
                  separator requirement: items for time (including Right 
                  Ascension) must be separated by the colon or comma, 
                  while items in degrees (including Declination) must be 
                  separated by the comma. In general, only the first item 
                  (hours or degrees) is required and a decimal fraction 
                  is allowed for all items. If you press RETURN for an 
                  item, the data for that item will be left unchanged.

                  When entering data manually, the parameters for proper 
                  motion are requested. Press RETURN to enter zero. These 
                  data are used by ASTROCLK to calculate the current 
                  apparent equatorial coordinates on the Tracking Display 
                  and are also used if the coordinates are precessed from 
                  one epoch to another using Function Key F8. This 
                  information is given for many stars in star catalogs 
                  such as SKY CATALOGUE 2000.0. However, note that 
                  ASTROCLK requires this information in SECONDS PER 
                  JULIAN CENTURY (36525 days) and not all references use 
                  the same units; SKY CATALOGUE 2000.0, for example, uses 
                  SECONDS PER YEAR which must be converted prior to input 
                  into ASTROCLK.

         ALT-F5   Because of its usefulness, the coordinates of the star 
   ASTROCLK Astronomical Clock and Celestial Tracking Program        Page 23


                  POLARIS (Alpha Ursa Minoris), the pole star, are hard 
                  coded into ASTROCLK on Function Key ALT-F5. POLARIS is 
                  often used for navigation and for the initial alignment 
                  of celestial telescopes and satellite dishes. Press 
                  this key and the coordinates for POLARIS are 
                  automatically entered and the display mode is switched 
                  to the Target Tracking Display.

             F6   Set new LOCAL COORDINATES. All entries are in degrees 
                  and require the comma as separator between the items. A 
                  decimal fraction is allowed for any item, and only the 
                  first item (degrees) is required. See the section 
                  SETTING LOCAL AND DESTINATION COORDINATES for details.


                  If file ASTROCLK.CTY (or an alternate city file) is 
                  present, it may be used to read the coordinates for a 
                  selection of cities. Enter the name of the location 
                  desired in upper or lower case. Only letters sufficient 
                  to uniquely identify the location are required. Press 
                  RETURN to ACCEPT the displayed location; press SPACE to 
                  search for the next match. Press ESC during the search 
                  to cancel the search and leave the local coordinates 
                  unchanged. If no match can be found, a CAUTION message 
                  will be displayed at the lower left of the screen. 
                  Press RETURN to continue; the local coordinates will be 
                  left unchanged.

                  To enter coordinates manually, press RETURN when 
                  prompted for the name. Then enter the LONGITUDE, 
                  LATITUDE and ELEVATION, followed by the NAME of the 
                  location. 

                  NOTE: Additional city files may be available from time 
                  to time on my BBS or by mail; see the end of the 
                  section A BRIEF EDITORIAL for the BBS telephone number 
                  and my address.

        SHIFT-F6  Set DESTINATION COORDINATES for use with navigation 
                  functions. Operates in all respects like F6 above 
                  except that the destination coordinates are set rather 
                  than the local coordinates, and you may enter "*" 
                  instead of a name to set the DESTINATION coordinates to 
                  the current LOCAL coordinates. 

         ALT-F6   Set LOCAL CONDITIONS for Elevation, Temperature, and 
                  Pressure. Allows the user to set these conditions to 
                  determine horizon dip and refraction. Automatic con-
                  version between metric and English units is performed. 

             F7   Set DISPLAY FORMAT for the main display window and Local 
                  Coordinates window. When the program is started, all 
                  angles and times on the main display window (other than 
                  large character times) and in the Local Coordinates 
                  window are shown in Degrees/Hours-Minutes-Seconds 
   ASTROCLK Astronomical Clock and Celestial Tracking Program        Page 24


                  format. Press F7 to cycle between display formats; the 
                  three available formats are:

                       ANGLES              TIMES
                       ------------        -----------
                       DDD MM SS.SS        HH:MM:SS.SS
                       DDD MM.MMMM         HH:MM.MMMM
                       DDD.DDDDDD          HH.HHHHHH

                  Press ALT-F7 to change Target Display coordinates from 
                  Right Ascension (hours) to Sidereal Hour Angle 
                  (degrees) and from Hour Angle (hours) to Greenwich Hour 
                  Angle (degrees), preferred by navigators and given in 
                  references such as the Astronomical Almanac. Press ALT-
                  F7 again to return to the original format. Declination 
                  is not affected. See also the section TARGET TRACKING 
                  DISPLAY for further discussion.

             F8   PRECESS Internal Star Database. This function allows 
                  the user to precess (adjust for different epochs) the 
                  current target data and the preset star database in the 
                  program. Upon startup, all data are set for epoch 
                  J2000.0, the current standard epoch. Press the "Y" key 
                  to make the precession calculations or press RETURN to 
                  cancel the calculations and leave all data unchanged.

                  If you proceed, press RETURN to restore all data to 
                  Epoch J2000.0 or enter the desired new epoch. The new 
                  epoch may be entered in any of the following formats:

                       dd,mm,yyyy          Calendar Date
                       JDnnnnnnn.nnnnnn    Julian Date
                       DJDnnnnnn.nnnnnn    Julian Date (J1900.0)
                       MJDnnnnnn.nnnnnn    Modified Julian Date
                       Jyyyy.yyy           Julian Epoch
                       Byyyy.yyy           Besellian Epoch
                       +nnn                Add nnn days to Current JD
                       -nnn                Subtract nnn days from Cur JD
                       *                   Current Julian Date and Time
                       #                   Current Julian Date @ 0h UT

                  Lower case letters (yyyy, nnnnnn, etc.) represent 
                  numbers while upper case letters (JD, J, etc.) are used 
                  to designate the data format being used. The calendar 
                  date method assumes the Julian or Gregorian calendar as 
                  determined by the date and the Calendar Flag (See ALT-
                  F10, Setting Program Options). Except for the calendar 
                  date method, any number of digits to the right of the 
                  decimal point may be input although more than about six 
                  will not be significant. Regardless of the data format 
                  used for input, the date is internally converted to the 
                  corresponding Julian Date for use in the precession 
                  calculations. The current ASTROCLK internal database 
                  epoch is always shown in the Target Tracking Display, 
                  Display Mode 0, and in the initial Precession 
   ASTROCLK Astronomical Clock and Celestial Tracking Program        Page 25


                  instructions when using Function Key F8.

                  Care should be taken when manually entering data whose 
                  epoch is different from that of the internal database. 
                  In order to maintain consistent data within ASTROCLK, 
                  the internal star database should first be precessed to 
                  a data epoch, then manual data referenced to that epoch 
                  should be entered. After that, all data may be 
                  precessed to the final epoch; using this procedure, 
                  both the manually entered data as well as the internal 
                  data will always refer to the same epoch.

                  For example, to track a target using Epoch J2000.0 
                  coordinates when the available catalog data is for 
                  Epoch B1950.0, first precess the internal star data to 
                  B1950.0 using F8, next enter the target Right 
                  Ascension, Declination, Name from the catalog, and the 
                  proper motion in Right Ascension and Declination (if 
                  known) using F5 (and F6 for manual entry). Finally, 
                  again use F8 to precess all data back to Epoch J2000.0 
                  (or any desired epoch). Thereafter, F8 may be used as 
                  many times as desired to precess the database.

             F9   DOS SHELL. This function invokes a copy of the MS-DOS 
                  executive, COMMAND.COM, and allows the user to enter 
                  any legal DOS command. COMMAND.COM must be available or 
                  ASTROCLK will ignore the request and continue normal 
                  operation. Since COMMAND.COM must reside in available 
                  memory in addition to ASTROCLK, use of a large RAM DISK 
                  or TSR program may cause the DOS shell to fail. The MS-
                  DOS prompt is displayed and the computer performs in 
                  most respects exactly as usual. However, far less 
                  memory is available and therefore programs which 
                  require very large amounts of memory for their 
                  execution may not operate properly with the SHELL. 

                  Enter EXIT to return to ASTROCLK and resume operation 
                  with all data and parameters unchanged.

                  SHIFT-F9 may be used to automatically executa a preset 
                  DOS command or batch file. The DOS command is set using 
                  ALT-F10, SETTING PROGRAM OPTIONS, and is saved in file 
                  ASTROCLK.INI. If a DOS command has been set, the 
                  command is executed and upon completion ASTROCLK is 
                  automatically resumed. This command has the same 
                  restrictions and comments as the normal F9 command 
                  above; the only difference is the execution of a preset 
                  DOS command and automatic return to ASTROCLK. The 
                  default is no action.

                  ALT-F9 may be used to automatically execute the USNO 
                  Interactive Computer Ephemeris (ICE) or the USNO Floppy 
                  Almanac (FA); see the section USNO EPHEMERIS PROGRAMS 
                  for more complete information. ALT-F9 will execute the 
                  selected USNO program if the appropriate software has 
   ASTROCLK Astronomical Clock and Celestial Tracking Program        Page 26


                  been installed in the computer AND if the appropriate 
                  ephemeris has been selected and its path set using ALT-
                  F10, SETTING PROGRAM OPTIONS. 

             F10  Function Key F10 provides navigational calculations 
                  using two methods: DEAD RECKONING and SIGHT REDUCTION. 
                  For an observer in motion, ASTROCLK also calculates the 
                  current position based upon the last "fix" and the 
                  observer's course and speed. See the section CELESTIAL 
                  NAVIGATION for details.

                  ALT-F10 is used to set or change various ASTROCLK 
                  program options. See the following section, SETTING 
                  PROGRAM OPTIONS, for details.

            0-9   Select Display Window Mode. The system starts out with 
                  LOCAL STANDARD/DAYLIGHT TIME displayed in large 
                  characters. In the United States, the correct time zone 
                  name (i.e. "PACIFIC") replaces the word "LOCAL". Press 
                  the number key associated with each display mode to 
                  change to that mode. (Use the numbers at the top of the 
                  keyboard rather than the number keys on the keypad at 
                  the right unless NUMLOCK is ON.) The available numeric 
                  modes and alphabetic commands are:

                  1    Local Standard or Daylight Time (LST/LDT)
                  2    Coordinated Universal Time (UTC)
                  3    Local Mean Sidereal Time (LMST)
                  4    Greenwich Mean Sidereal Time (GMST)
                  5    Local Mean Solar Time
                  6    Perpetual Calendar
                  7    Julian Date Information
                  8    Precision Time Display
                  9    Planetary Data
                  0    Target Tracking Display

                  N    Select NAVIGATION Display Mode

                  P    Select PLANET or MINOR PLANET
                       (forces display mode 9 or 0)

                  A    Alarm Countdown *
                  S    Start/Stop Interval Timer *
                  T    Interval Timer *
                  Z    Stop and Reset Interval Timer *

                       *  See the section ALARM AND INTERVAL TIMER 
                          OPERATIONS for information on these modes.

                  While in display mode 0, Target Tracking, use the UP 
                  and DOWN arrow keys to select the next or the previous 
                  Standard Navigational Star. PgUp and PgDn increase or 
                  decrease the selected star number by 10. Use F5 to 
                  input a new star number directly.

   ASTROCLK Astronomical Clock and Celestial Tracking Program        Page 27


                  While in display modes 1 through 5, the large clock 
                  displays, use the UP and DOWN arrow keys to select the 
                  dual-time displays and the HOME key to return to 
                  single-time display. See the section DUAL-TIME DISPLAYS 
                  for further information.

                  While in display mode 6, Perpetual Calendar, use the 
                  Left and Right arrow keys to change months, the Up and 
                  Down arrow keys to change years, and the PgUp and PgDn 
                  keys to change the years by decades. HOME returns the 
                  display to the current system date. Use F3 to input a 
                  new date or time directly.

                  While in display mode 8, Precision Time and Data 
                  Displays, press PgUp or PgDn to view the next Precision 
                  Time or Data Display. See the section PRECISION TIME 
                  AND DATA DISPLAYS for details.

                  While in display mode 9, Planetary Data, use the UP and 
                  DOWN arrow keys to change planets. See the section 
                  PLANETARY DATA DISPLAYS for further discussion.

                  Pressing "N" to select the Navigation Mode Display will 
                  result in an error message if navigation has not been 
                  enabled with Function Key F10. See the section 
                  NAVIGATION for further discussion.
   ASTROCLK Astronomical Clock and Celestial Tracking Program        Page 28



        SETTING PROGRAM OPTIONS

             Several ASTROCLK program options can be set using Function 
        Key ALT-F10. The options which can be set are: DAYLIGHT FLAG, 
        ZONE CORRECTION, COLOR FLAG, ICE/FA Flag, CALENDAR FLAG, external 
        FILE NAMES and PATHS, and PRESET DOS COMMAND. All of this 
        information is saved in file ASTROCLK.INI.
             The DAYLIGHT FLAG determines whether or not Daylight Time is 
        in effect. The ZONE CORRECTION allows the user to adjust for time 
        zones which do not agree with the calculated values. The CALENDAR 
        FLAG determines which of three calendar conventions to use; it is 
        initially set to the Gregorian Calendar (from October, 1582). A 
        sub-menu is displayed when using ALT-F10 with the current values 
        shown enclosed by square brackets, "[...]". Press the function 
        key corresponding to the option you wish to change or press 
        RETURN to resume normal program operation with the options as 
        shown. A typical display showing the default values for each item 
        is shown below:

             F1   DAYLIGHT FLAG:           [OFF]
             F2   ZONE CORRECTION:         [0.00]
             F3   COLOR FLAG:              [ON]
             F4   ICE/FA FLAG:             [0=ICE/FA Disabled]
             F5   CALENDAR FLAG:           [1=Gregorian @ 1582]
             F6   SET FILE NAMES & PATHS
             F9   SET DOS COMMAND
                  (no command has been entered)
             RETURN  Resume normal program operation

             When all changes have been made and the information 
        displayed on the menu is correct, press RETURN to resume normal 
        program operation. When you exit ASTROCLK, these options will be 
        saved in file ASTROCLK.INI and will automatically be restored the 
        next time you run the program.

        Setting the DAYLIGHT FLAG
        -------------------------

             The DAYLIGHT FLAG selects whether or not an additional hour 
        will be automatically added during the time zone calculation to 
        determine Coordinated Universal Time. The flag applies equally to 
        all time zones and the window label for local time will include 
        the word STANDARD if the flag is OFF, or the word DAYLIGHT if the 
        flag is ON. For example: PACIFIC STANDARD TIME or PACIFIC 
        DAYLIGHT TIME. If you wish to change the state of the flag, press 
        Function Key F1. The DAYLIGHT flag is OFF by default. Because the 
        date of switching to and from daylight time are different in 
        different countries and are sometimes changed for one reason or 
        another, ASTROCLK does not automatically set the state of the 
        flag. If the UT TIME ZONE OFFSET has been enabled, be sure to 
        correct that value using F10 when the DAYLIGHT FLAG is changed.
             If the DAYLIGHT FLAG is incorrectly set, all calculated 
        times and positions will also be incorrect. Do NOT use the 
        DAYLIGHT FLAG to adjust for an incorrect zone calculation; use 
   ASTROCLK Astronomical Clock and Celestial Tracking Program        Page 29


        the ZONE CORRECTION (see the following item) for that purpose. 
        You may, if you prefer, leave your computer clock always set to 
        local STANDARD time and the DAYLIGHT FLAG always off. However, 
        you may NOT set your computer clock to UTC (unless you are in 
        that time zone); set the computer clock correctly and use display 
        mode 2 to view UTC instead.

        Setting the ZONE CORRECTION
        ---------------------------

             The ZONE CORRECTION allows the user to make special 
        adjustments in the calculation of Coordinated Universal Time 
        (UTC) relative to Local Time. Some time zones are not an integral 
        number of hours offset from UTC; in other cases the actual 
        standard time for a particular location is different from that 
        calculated by ASTROCLK because of the irregular way time zones 
        have been defined locally. Some countries use "Double Summer 
        Time" which is two hours ahead of the standard time for the zone. 
        To change the current ZONE CORRECTION, press F2. The correction 
        must be entered in hours and decimal fraction, H.HH or -H.HH, and 
        is automatically rounded to the nearest 0.25 hours (15 minutes); 
        the maximum correction is restricted to the range -2.00 hours to 
        +2.00 hours. The ZONE CORRECTION is calculated in ADDITION to the 
        DAYLIGHT FLAG.
             IMPORTANT NOTE: Unlike the Daylight Flag, which remains 
        unchanged when you change local coordinates, the Zone Correction 
        will be reset to 0.00 hours any time you change the local 
        coordinates on the assumption that the Zone Correction is 
        unique to a given location. This also assures that when using 
        the external city file to change cities and load the coordinates 
        from the file, the Zone Correction will be reset. The default 
        value for the Zone Correction is 0.00 hours.

        Setting the COLOR FLAG
        ----------------------

             The COLOR FLAG allows you to switch between color, red, 
        green, and monochrome display. The COLOR mode uses various colors 
        for the display. The RED option sets all screen colors to red in 
        order to protect night vision if the computer is operated in a 
        darkened area. The GREEN option sets all screen colors to green; 
        this may help reduce eye fatigue during extended use. The OFF 
        (monochrome) mode is useful if you wish monochrome display or 
        white display on color monitors. Switching to any of the color 
        modes on some true monochrome systems may cause an error. See 
        also the section PROGRAM OPERATION for additional information on 
        the command line color options.
             To change the COLOR FLAG from one mode to the next, press 
        Function Key F3; the color changes for the new mode will take 
        effect immediately within the window but the balance of the 
        display will not be affected until you leave the Setting Programs 
        Options window by pressing the RETURN key.
             The state of the COLOR FLAG is saved in file ASTROCLK.INI 
        and the program will use the previously set color mode the next 
        time it is run. However, the command line color option (/M, /R, 
   ASTROCLK Astronomical Clock and Celestial Tracking Program        Page 30


        or /G), if present, always overrides the saved state of the COLOR 
        FLAG read from file ASTROCLK.INI.

        Setting the ICE/FA FLAG
        -----------------------

             The ICE/FA FLAG allows you to select between the following 
        three options for external USNO ephemeris programs:

             0 =  No external USNO ephemeris program is available. 
                  Pressing ALT-F9 will display an error message. 
                  (DEFAULT)

             1 =  The USNO Interactive Computer Ephemeris, ICE, is 
                  installed and will be executed by pressing ALT-F9. Be 
                  sure to set the ICE drive and/or path correctly!

             2 =  The USNO Floppy Almanac, FA, is installed and will be 
                  executed by pressing ALT-F9. Be sure to set the FA
                  drive and/or path correctly!

             Press F4 until the desired option is displayed. Do not 
        select one of the USNO ephemeris program options unless the 
        appropriate ephemeris files have been installed. See also the 
        section USNO EPHEMERIS PROGRAMS for additional information.

        Setting the CALENDAR FLAG
        -------------------------

             The CALENDAR FLAG allows you to select between the following 
        three calendar conventions:

             0 =  Strict Julian Calandar for ALL dates. Technically, this 
                  calendar is known as the Julian Proleptic Calendar for 
                  dates prior to 46 B.C. NOTE: The Julian Calendar may 
                  not be used in real time (see below).

             1 =  Julian Calendar switching to Gregorian Calendar in 
                  October, 1582 in accordance with standard astronomical 
                  convention (DEFAULT).

             2 =  Julian Calendar switching to Gregorian Calendar in 
                  September, 1752 corresponding to usage in Great Britain 
                  and her colonies (including the United States).

             Press F5 to change the flag until the desired calendar 
        convention is displayed. For additional information on the 
        various calendar conventions, see the section DATES AND THE 
        GREGORIAN CALENDAR.
             NOTE: Regardless of the calendar convention in effect, 
        ASTROCLK always assumes that the system clock is set to the 
        correct date. This means that only calendar flag values of 1 and 
        2 are permitted with the CLOCKS ON. ASTROCLK's internal date 
        functions are performed using the current Julian Date. Therefore, 
        switching from the Gregorian Calendar to the Julian Calendar for 
   ASTROCLK Astronomical Clock and Celestial Tracking Program        Page 31


        a modern date with the CLOCKS OFF will leave the Julian Date 
        unchanged but will change the calendar date to a new value, 
        correct for the strict Julian Calendar. However, if the clocks 
        are ON, they will automatically be set to OFF and a warning 
        message will be displayed. If you wish to use the program with 
        the Julian Calendar and the clocks running, use the SIMULATION 
        mode.

        Setting the FILE NAMES and PATHS
        --------------------------------

             In order to execute the help function and to utilize the 
        external data files and the USNO Interactive Computer Ephemeris 
        (ICE) or Floppy Almanac (FA), ASTROCLK must know what the file 
        names are and where to find them. The default condition is that 
        these files are all located in the current directory and that the 
        files have the following names:

                  ASTROHLP.EXE        External Help Program
                  ASTROCLK.CAT        External star catalog
                  ASTROCLK.MPC        External minor planet catalog
                  ASTROCLK.CTY        External city file
                  ICE.EXE             USNO Interactive Computer Ephemeris
                  FAnn.EXE            USNO Floppy Almanac (nn=88-99)

        There is a different file for each year for the USNO Floppy 
        Almanac. All files required by ICE or FA must be located in the 
        same directory as the .EXE file. A common drive and path may be 
        specified in the command line when starting ASTROCLK for the 
        first time.

                              ********************
                              *  IMPORTANT NOTE  *
                              ********************

             Once ASTROCLK has been executed the first time, the drive 
        and path information are saved in the program initialization 
        file ASTROCLK.INI. Thereafter, ASTROCLK uses the information 
        in ASTROCLK.INI and overrides any drive or path specification
        entered on the command line. You may use ALT-F10 and then F6 to 
        change the drive and/or subdirectory from within ASTROCLK, or you 
        may delete file ASTROCLK.INI at the DOS prompt to start over.

                                    * * * * *

             Since two of the external data files, ASTROCLK.CAT and 
        ASTROCLK.CTY, are conventional ASCII files which may be edited by 
        the user, a provision is included here to permit the user to 
        specify an alternate file name for either of these files, 
        including drive and path. For example, you might wish to use a 
        special city file when traveling in Europe. More ambitious users 
        may wish to prepare their own external star catalogs.
             The current STAR CATALOG, MINOR PLANET CATALOG, and CITY 
        FILE names are shown on the menu, in that order. If a drive 
        and/or path was specified with the command line, they will also 
   ASTROCLK Astronomical Clock and Celestial Tracking Program        Page 32


        be shown. If no drive or path is shown, ASTROCLK assumes the 
        current drive and directory. To change one or more file names, 
        press F6 and enter the new name when prompted or press RETURN to 
        leave a name unchanged. You may include a drive and path 
        specification if desired. Enter SPACE to restore the file name to 
        the default. (A long path specification may exceed the width of 
        the display window but it will be processed correctly.)
             For convenience, an additional file, MESSIER.CAT, is 
        available with the data for the 109 Messier objects only. The 
        same data is included in file ASTROCLK.CAT but at the end of that 
        long file. If you are content with the 57 internal USNO stars 
        plus Polaris and just wish to add the Messier objects, use 
        MESSIER.CAT and then substitute it for ASTROCLK.CAT using ALT-F10 
        and then F6. This will substantially reduce the catalog search 
        time, especially on floppy disk based systems. M40 has always 
        been missing and the entry for that item contains only null data.
             An alternate city file, USCITIES.CTY is available which 
        includes some 718 U.S. cities with the geographical coordinates 
        given to a higher accuracy than the standard ASTROCLK.CTY.
             Other special city files and star catalogs may also be
        available from time to time on my Bulletin Board System (BBS). 
        See the section A BRIEF EDITORIAL near the end of this document 
        for information on the BBS.

             THE "EASY" METHOD OF SETTING PATHS: If you do not understand 
        paths and subdirectories or simply do not wish to alter 
        ASTROCLK's default setup, simply make sure that all ASTROCLK 
        files (and the USNO ICE or FA files, if you have them) are 
        located on the same drive and directory. I recommend that the 
        files be located on the selected drive in directory ASTROCLK; see 
        your DOS manual for information on how to create the directory 
        and copy the ASTROCLK files to that directory. Then run ASTROCLK 
        from the ASTROCLK directory using the following command (which 
        assumes drive C:):

                  ASTROCLK C:\ASTROCLK

        All drive and path information will be saved in file ASTROCLK.INI 
        for subsequent uses of the program. Then, if you execute ASTROCLK 
        from the ASTROCLK directory, the program will be able to find all 
        its required files.

             However, it is often necessary or convenient to have some 
        files, especially the Floppy Almanac files, located in another 
        drive and/or subdirectory. This is particularly true for floppy 
        disk based systems where the individual disk capacity may prevent 
        all files from being on the same disk. The drive and path for 
        ASTROCLK and for the USNO Interactive Computer Ephemeris (ICE) or 
        Floppy Almanac (FA) may be separately set using F6, and specific 
        file names (including drive and directory if desired) may be set 
        for the external star catalog, minor planet catalog, and city 
        files.
             When setting the ASTROCLK and ICE or FA paths, ONLY THE 
        DRIVE AND PATH ARE SPECIFIED. A backslash ("\") should be the 
        first character of each path except for a blank path; a CAUTION 
   ASTROCLK Astronomical Clock and Celestial Tracking Program        Page 33


        warning message will be displayed if you do not include it. Do 
        NOT add a backslash at the end of the path. Unless you include a 
        drive specification such as "D:", ASTROCLK assumes that all files 
        are located on the current drive. If you include a drive 
        specification with the ICE or FA path, you must also include a 
        drive specification with the ASTROCLK path; a CAUTION warning 
        message will be displayed if you do not include it.
             Thus, if your ICE/FA and related files are in drive 
        D: and path \FA, enter "D:\FA", followed by RETURN, for the 
        ICE/FA path. Setting the ICE/FA path not only enables ASTROCLK to 
        locate the ICE.EXE or FAnn.EXE files, it also tells ASTROCLK 
        where to write the file ICE.DFT or FA.DFT (which determines the 
        default conditions for the program).
             The external file names default to ASTROCLK.CAT, 
        ASTROCLK.MPC and ASTROCLK.CTY, and ASTROCLK also assumes by 
        default that they are all located in the ASTROCLK path. Enter an 
        alternate file name for one or more files if desired. You may 
        include the drive and/or subdirectory if they are different from 
        ASTROCLK's values. Enter a SPACE to reset the file name to the 
        default name.

        Setting the PRESET DOS COMMAND
        ------------------------------

             This feature, requested by several users, allows you to 
        enter a preset DOS command which will be executed from ASTROCLK 
        each time you press SHIFT-F9. The current preset DOS command is 
        shown on the screen; if no command has been entered or read from 
        file ASTROCLK.INI, the following message will appear:

                  (no command has been entered)

        Press F9 to select this option and then enter the desired command 
        or the name of the batch file (without the .BAT portion of the 
        file name) which you wish to be executed. Press RETURN by itself 
        to clear the preset DOS command. NOTE: If you select this option 
        by mistake, you must re-enter the desired DOS command or it will 
        be cleared.
             Once the desired DOS command has been entered, return to 
        ASTROCLK and test the command by pressing SHIFT-F9. Bear in mind 
        that very large programs may require more memory than is 
        available under the SHELL used by ASTROCLK to execute DOS 
        programs. Further, using TSR (Terminate and Stay Resident) 
        programs may leave insufficient memory to use this feature or may 
        cause programs to operate unpredictably.
   ASTROCLK Astronomical Clock and Celestial Tracking Program        Page 34



        SETTING LOCAL/UT/TDT TIME AND DATE

             ASTROCLK has three basic modes of operation: real time, 
        simulated real time, and static. In the real time mode, the 
        clocks are running synchronized to the system clock and the data 
        displayed are calculated every second (computer calculation time 
        permitting). The simulation mode is the same as real time except 
        that ASTROCLK uses a time previously set with Function Key F3 as 
        its reference. Using a Zenith Z-183 laptop computer not equipped 
        with a coprocessor, ASTROCLK is able to make most calculations 
        (except for Tracking and Precision data) within one second. 
        Compared to a Zenith Z-248 8 MHz AT-compatible computer with a 
        math coprocessor, the computational delays are noticeable. 
        Provided the local time, date and coordinates have been properly 
        set, the data reflect the correct real time (or simulated real 
        time) parameters. In the static mode, the data are held at the 
        values for the specified time.
             Except in the Navigation Mode, an algorithm is used to 
        automatically calculate the time offset from UTC, Coordinated 
        Universal Time based upon the longitude of the local coordinates. 
        UTC is roughly equal to  Greenwich Mean Time (GMT) for years 1925 
        and later. The results of this calculation are shown as UTC ZONE 
        (for example, -118 degrees yields UTC -8.0 for Pacific Standard 
        Time in Southern California), and are used in all subsequent time 
        and position calculations. All calculations are based upon 
        Standard Time. If Daylight Time is in use AND your computer clock 
        is set to Daylight Time, use Function Key ALT-F10, SETTING 
        PROGRAM OPTIONS, and set the DAYLIGHT FLAG ON to automatically 
        adjust the times. To return to Standard Time, set the DAYLIGHT 
        FLAG OFF. ASTROCLK does not perform any date tests to verify the 
        validity of the DAYLIGHT FLAG setting.
             Because of the strange ways time zones have been drawn, the 
        automatic time zone calculation may not always produce the 
        desired result. The calculated time IS the correct time based 
        upon the division of the world into 24 equal time zones. However, 
        for political reasons or for local convenience, time zones often 
        do not excatly follow the designated meridians. If a location is 
        more than 7-1/2 degrees East or West of the 15 degree meridian 
        corresponding to the local standard time, the time calculations 
        will be an hour in error.  Use the ZONE CORRECTION with ALT-F10, 
        SETTING PROGRAM OPTIONS, to correct for this problem to the 
        nearest fifteen minutes. Some time zones are not set at an 
        integral number of hours offset from UTC, fortunately none of 
        them in the United States. A correction of from -2.00 hours to 
        +2.00 hours will be accepted in order to accommodate both time 
        zone errors and double daylight times. For U.S. locations not 
        requiring this special correction, ASTROCLK will automatically 
        display the correct zone name, Eastern, Pacific, etc.
             In the Navigation Mode, the calculation of times is handled 
        slightly differently. Because the computer may move from one time 
        zone to another, the Navigation Mode requires that the UT TIME 
        ZONE OFFSET, the difference between the computer's clock and 
        Universal Time (UT), be entered using Function Key F10. ASTROCLK 
        then automatically converts the computer clock to UT before 
   ASTROCLK Astronomical Clock and Celestial Tracking Program        Page 35


        making adjustments for the current longitude (whether calculated 
        or manually entered). This permits the computer to move freely 
        from time zone to time zone without resetting the computer's 
        internal clock. However, there is as usual no free lunch; because 
        the local time is strictly dependent upon the current longitude, 
        no ZONE CORRECTION for time zones which do not correspond to the 
        calculated time is permitted. Any ZONE CORRECTION in effect when 
        the UT OFFSET is set will be cleared. On the other side of the 
        coin, once the UT OFFSET has been set ASTROCLK's local 
        coordinates may be set as desired and the current correct local 
        time will be calculated and displayed and UT TIME will remain 
        constant. ASTROCLK will adjust ALL local times by one hour if the 
        DAYLIGHT FLAG is set; given that the dates when daylight time is 
        in effect vary considerably around the world, users may find it 
        more convenient to leave the DAYLIGHT FLAG off when away from 
        their "home" time zone(s), turning it on only when certain of the 
        local standard. See also the discussion of the UT TIME ZONE 
        OFFSET in the NAVIGATION section.
             When used in the static mode, the clocks are stopped. The 
        user may enter any desired location or time/date and all 
        calculations will be made using that data. Note that West 
        longitudes and South latitudes must be entered as negative 
        numbers for ASTROCLK. (CAUTION: Some texts and institutions do 
        not observe the same sign conventions!) The basic calculations in 
        ASTROCLK are based upon formulae accurate for Epoch J2000.0. 
        Negative dates, that is dates "B.C.", display in RED (BLINK in 
        all monochrome modes) and there is no year 0000; the sequence of 
        years near zero is -2, -1, 1, 2, etc. The accuracy of some of the 
        celestial data will decrease as the time difference from Epoch 
        J2000.0 increases. 
             Although UTC and UT (=UT1) are not the same, they are 
        maintained to within 0.9 seconds of each other by the occasional 
        insertion of Leap Seconds at the end of June or December. In 1988 
        the difference is typically less than 0.2 seconds. While software 
        programs are available to precisely set a computer's clock using 
        telephone signals from NBS, this accuracy cannot usually be 
        maintained for extended periods of time. In any event, frequent 
        calls to NBS are impractical for most of us by reason of cost. A 
        more cost effective solution is to use the Heath/Zenith GC-1000 
        Most Accurate Clock and its optional software to synchronize the 
        computer's clock. The GC-1000 is a combination receiver and clock 
        and when equipped with an RS-232 interface and external antenna, 
        it can maintain UTC time to within 10 milliseconds.
             I have therefore elected to treat UTC as equal to UT for 
        time and date displays and have actually assumed UT time and date 
        in all but one case: the correct UTC time relative to UT is 
        calculated and displayed on Precision Time Display #1 but it is 
        otherwise not used. All other times and dates are referenced to 
        UT rather than to UTC. This minor technical error represents a 
        compromise between technical accuracy and ease of use.
             While the times displayed by ASTROCLK in the various small 
        windows are rounded to the nearest second, any time (Local, UT, 
        or TDT) may be entered using Function Key F3 to a precision of 
        approximately 0.0001 seconds and will be used to that precision 
        in the various calculations. Compare the times shown in the small 
   ASTROCLK Astronomical Clock and Celestial Tracking Program        Page 36


        windows with those in the Precision Time Display #1. Except for 
        some items in the Precision Time Displays, this additional 
        precision is usually not significant. See the section PRECISION 
        AND ACCURACY TESTS for additional comments.


        Setting the LOCAL/UT/TDT Time

             The time entry format is very flexible and for convenience 
        will accept either the traditional colon (":") or the comma (",") 
        as the separator between hours and minutes or minutes and 
        seconds; the examples are shown with the colon only. Each item 
        (hours, minutes, or seconds) can accept a decimal fraction 
        although normally only the last item entered would have a 
        fractional part. Time entries are ALWAYS made using the 24-hour 
        convention. The following are all acceptable time entries:

                  HH                       Hours
                  HH.HHHHHH                Hours + fractional hours
                  HH:MM                    Hours:Minutes
                  HH:MM.MMMM               Hours:Minutes + frac mins
                  HH:MM:SS                 Hours:Minutes:Seconds
                  HH:MM:SS.SS              Hours:Minutes:Seconds + frac
                  
             The "standard" date input format requires the day, month, 
        and year (in that order, European style, and separated by commas) 
        in either of the following two formats:

                  DD,MM,YYYY
                  DD.DDD,MM,YYYY

        The first format specifies the date to be used with the existing 
        or just input time; unless the letter "U" or "T" has been 
        appended to the time input (see below), the date is the LOCAL 
        date. The second format, containing a fractional day (including 
        "." alone or ".0") specifies a UT date with the time implicit to 
        allow the astronomical convention where dates are often given in 
        the form "1988 JAN 1.5"; this would be entered as "1.5,1,1988". 
        The time input is ignored with this format (press RETURN). The 
        fractional part may have as many digits as desired, but more than 
        about six digits usually are not significant.
             It is sometimes convenient to set the time and date using 
        UT (=UT1) data. This avoids having to make the conversions 
        mentally. If you add the letter "U" at the end of the time or 
        date entry, ASTROCLK will perform the appropriate time or date 
        conversions automatically, based upon the current settings of the 
        DAYLIGHT FLAG and ZONE CORRECTION. If you add "U" to your time 
        input to enter UT time, ASTROCLK assumes that you are also 
        entering UT date. If you enter a fractional part of a day as part 
        of the date input, the time input is ignored and UT date is 
        assumed (see the preceeding paragraph).
             As an example, to set the time and date to 9:44:30 UT on 
        November 13, 1978, use the following entries:

                  9:44:30U            (UT time)
   ASTROCLK Astronomical Clock and Celestial Tracking Program        Page 37


                  13,11,1978          (UT date)
    
        Alternatively, the same time and date may be input by pressing 
        RETURN for the time, and using the following date entry (with the 
        fractional part of the day representing the desired time):

                  13.405903,11,1978   (UT date, time implicit)

             If Terrestrial Dynamical Time (or Ephemeris Time prior to 
        1984) is desired, add the letter "T" (or "E") at the end of the 
        time entry. ASTROCLK automatically selects TDT or ET based upon 
        the date regardless of the letter used to designate the time 
        during input. Note that the displayed UTC DATE may not correspond 
        to that input if the time is within the period Delta T (TDT-UT) 
        of midnight. ASTROCLK automatically adjusts the date to agree 
        with the information input and near midnight this can be 
        confusing to the user!


        Setting the LOCAL/UT Date

             The date input routine will also permit the entry of the 
        Julian Date (JD), Dublin Julian Date (DJD), Modified Julian Date 
        (MJD), Truncated Julian Date (TJD), or Greenwich Sidereal Date 
        (GSD) by prefixing the date with the appropriate two or three 
        letters followed by the desired date. Whenever letters are used, 
        they may be input in upper or lower case. Note that when an 
        integer GSD is entered (no fraction to the right of the decimal 
        point), the resulting UT time is the Greenwich Transit of the 
        Mean Equinox at 0h GMST for that date. The following formats are 
        available:

                       JDddddddd.dddddd         Julian Date
                      DJDddddddd.dddddd         Dublin Julian Date
                      MJDddddddd.dddddd         Modified Julian Date
                      TJDddddddd.dddddd         Truncated Julian Date
                      GSDddddddd.dddddd         Greenwich Sidereal Date

             Decimal fractions of a day may also be included, as shown 
        above and in the subsequent examples, but more than six digits to 
        the right of the decimal point will probably not be significant 
        in most calculations. If the current date plus or minus a number 
        of days is desired, the form +nnn or -nnn may be used with "nnn" 
        being the desired number of days. Entering "#" alone will yield 
        the current Julian Date at 00:00:00 UT; entering "*" alone will 
        yield the exact current Julian Date (useful for precession 
        calculations with Function Key F8). Examples:

                       +3                       Current JD + 3 days
                       -10                      Current JD - 10 days
                       +1.5                     Current JD + 1.5 days
                       #                        Current JD @ 00:00:00 UT
                       *                        Current JD
                  
             Similarly, dates may be input as Julian or Besselian Epochs 
   ASTROCLK Astronomical Clock and Celestial Tracking Program        Page 38


        by prefixing the epoch with the letter "J" or "B" respectively. 
        Two formats are available:

                       Jyyyy.yyyyyy             Julian Epoch
                       Byyyy.yyyyyy             Besselian Epoch

             Finally, inspired by the desire to interpret dates on images 
        during Voyager 2's close encounter with Neptune in August 1989, 
        dates may be input as the current Day-of-the-Year, with January 1 
        being Day 1. Note that this method may ONLY be used for the 
        year currently set and displayed. UT Hours, minutes and seconds 
        may be included if desired, as shown by the following format 
        examples:

                       Dnnn[.nnnn]              Day Number
                       Dnnn:hh[.hhhh]           Day + UT Hours
                       Dnnn:hh:mm[.mm]          Day + UT Hours+Minutes
                       Dnnn:hh:mm:ss[.ss]       Day + UT Hrs+Mins+Secs

             When these special forms of date input are used, you may 
        press RETURN in response to the time prompt since UT time is 
        implicit in the date format; any time that is input will be 
        overridden and the implicit time associated with the date used 
        instead. All of these date formats are calculated in Display Mode 
        7, Julian Date Information, and that display may be used to 
        easily convert dates from one format to another; while in Display 
        Mode 7, use F3 to enter the date in one format and read the 
        desired conversion on the screen. For example, the following date 
        entries are equivalent to July 2, 1988 at 03:00:00 UT to within a 
        few seconds:

                  JD2447344.625
                   DJD32324.625
                   MJD47344.125
                    TJD7344.125
                 GSD2454045.903811

                      J1988.5
                      B1988.501032

             NOTE: If you enter a date as a simple number, greater than 
        50 and without a letter or sign prefix such as "JD" or "+", 
        ASTROCLK assumes that you wish to enter the Julian Date and 
        simply neglected to include the "JD" prefix. The program 
        therefore interprets such entries (up to the first comma, if 
        present) as Julian Dates and no warning or error message is 
        generated. (ASTROCLK versions prior to 8831 would sometimes 
        generate a QuickBASIC error and abort ASTROCLK in this situation 
        because the number was interpreted as the day of the month.)
   ASTROCLK Astronomical Clock and Celestial Tracking Program        Page 39



        SETTING LOCAL AND DESTINATION COORDINATES

             Before most of the data displayed by ASTROCLK can be of any 
        practical use, you must set your own geographical coordinates 
        into the program using Function Key F6. On startup, ASTROCLK uses 
        the coordinates for Rancho Palos Verdes, California, near Los 
        Angeles. If you do not know your coordinates, I recommend that 
        you consult Goode's World Atlas, 17th Edition, which includes an 
        extensive Index with longitudes and latitudes of some 30,000 
        cities and other locations worldwide. All coordinates are given 
        to one minute of arc, and this is the only atlas I know which 
        includes this information. NOTE: In spite of the format used for 
        the coordinates in Goode's, 118.34 for example, the portion to 
        the right of the decimal point represents minutes NOT decimal 
        parts of a degree. See the BIBLIOGRAPHY for the full reference.
             With the addition of navigation functions to ASTROCLK, 
        Function Key SHIFT-F6 has been included to allow destination data 
        to also be read from the same "city file". The operation of 
        SHIFT-F6 is identical to normal operation of Function Key F6 
        decribed below except that the DESTINATION name and geographic 
        coordinates are set rather than the LOCAL name and coordinates. 
        The destination data are disabled when ASTROCLK is first started. 
        See the section CELESTIAL NAVIGATION for additional discussion.
             The following prompt will appear in the main window after 
        pressing F6:

                  SET LOCAL COORDINATES

                  Enter CITY NAME to search for in file
                     \ASTROCLK\ASTROCLK.CTY

                  Enter desired name:  _

                  Match starts at left of name. Prefix input
                  with '/' to match input anywhere within
                  the name. Matches are case insensitive.

                  Press RETURN for MANUAL data entry.

        When using SHIFT-F6, the display is the same except that the 
        title includes the word DESTINATION instead of LOCAL and you may 
        also enter the name as "*" to set the DESTINATION coordinates to 
        the current LOCAL coordinates. The file name shown in the example 
        is the standard city file supplied with ASTROCLK.
             Using file ASTROCLK.CTY, you may automatically enter the 
        data for any of the cities included in that file. Other "city 
        files" may be available or may be created as required. Enter the 
        name or first part of the name of the desired city. Only letters 
        sufficient to unambiguously select the city are required, either 
        upper or lower case may be used, and spaces are significant. For 
        example, "k" is sufficient for "Kansas City" since there is 
        currently only one city beginning with the letter K, but "san f" 
        is required to distinguish "San Francisco" from "San Antonio", 
        "San Diego", etc. The search stops at the first match, so "san" 
   ASTROCLK Astronomical Clock and Celestial Tracking Program        Page 40


        would first match "San Antonio" and you would have to press the 
        space bar several times before you reached "San Francisco".
             Alternatively, you may prefix the name you enter with the 
        "/" character (without the quotation marks) and ASTROCLK will 
        attempt to match your input anywhere within the file's city 
        names. For example, a special navigation city file of VOR's, 
        USWEST.VOR, includes the three letter code designation for each 
        VOR in addition to the full name; the code for the Los Angeles 
        VOR is "LAX". To select Los Angeles by the code designation, you 
        may enter "/lax" (again without the quotation marks and in either 
        upper or lower case). Using this method with too short or simple 
        a designation may find many qualifying matches.
             For each qualifying match found, ASTROCLK presents the data 
        read from the file and awaits your choice: press RETURN to ACCEPT 
        the data shown, or press the SPACE BAR to look for the next 
        match. If in doubt, consult the list below or print the file 
        ASTROCLK.CTY to obtain the current list of cities. ASTROCLK.CTY 
        is an ASCII file and may be edited to modify the data; use non-
        document mode and observe the comma-delimited format when making 
        additions or changes.
             Three geographical locations are "hard coded" (for my own 
        personal convenience) and may be selected by entering the 
        following abbreviations for the local name (upper or lower case):

                       RPV       Rancho Palos Verdes, CA
                       CAL       Calaveras County, CA
                       USNO      U. S. Naval Observatory, Washington, DC

             To manually enter local coordinates (instead of searching 
        the external file), press RETURN when asked for the city name. 
        Then enter LONGITUDE, LATITUDE, ELEVATION, and NAME when 
        requested. WEST longitude and SOUTH latitude must be entered as 
        NEGATIVE numbers. Press RETURN to skip an entry and leave it 
        unchanged except ELEVATION which is reset to zero.
             A special program, MAPCOORD, is available from my bulletin 
        board system which may be used to generate city files or to 
        append new entries to an existing city file. Other city files, 
        including file USWEST.VOR mentioned above, are also available.
             The listing of file ASTROCLK.CTY which follows gives the 
        approximate longitude and latitude for selected cities in the 
        United States and Canada. All coordinates are given in degrees to 
        two decimal places and have been estimated to an accuracy of 
        about 0.5 degrees or better. NOTE: West longitudes are shown as, 
        and must be entered as, as negative numbers.
   ASTROCLK Astronomical Clock and Celestial Tracking Program        Page 41


                          Listing of File ASTROCLK.CTY


             CITY                       LONGITUDE      LATITUDE
             --------------------------------------------------
             Albuquerque, NM              -106.50         35.00
             Atlanta, GA                   -84.25         33.75
             Baltimore, MD                 -76.62         39.25
             Birmingham, AL                -85.83         33.50
             Boston, MA                    -71.08         42.17
             Buffalo, NY                   -78.83         42.92
             Chicago, IL                   -87.67         41.83
             Cleveland, OH                 -81.67         41.50
             Columbus, OH                  -83.00         39.95
             Dallas, TX                    -97.83         32.83
             Denver, CO                   -105.00         39.75
             Detroit, MI                   -83.00         42.33
             El Paso, TX                  -106.42         31.78
             Ft. Lauderdale, FL            -80.08         26.17
             Ft. Worth, TX                 -97.33         32.75
             Greensboro, NC                -79.75         36.08
             Hartford, CT                  -72.67         41.75
             Honolulu, HI                 -157.83         21.33
             Houston, TX                   -95.33         29.75
             Indianapolis, IA              -86.17         39.75
             Kansas City, KS/MO            -94.58         39.12
             Las Vegas, NV                -115.17         36.17
             Los Angeles, CA              -118.25         34.00
             Louisville, KY                -85.75         35.25
             Memphis, TN                   -90.08         35.17
             Miami, FL                     -80.17         25.75
             Milwaukee, WI                 -88.00         43.00
             Minneapolis, MN               -93.25         45.00
             New Orleans, LA               -90.08         30.00
             New York, NY                  -73.50         40.50
             Newark, NJ                    -74.17         40.70
             Norfolk, VA                   -76.33         36.83
             Oakland, CA                  -122.25         37.75
             Oklahoma City, OK             -97.50         35.00
             Philadelphia, PA              -76.17         39.92
             Phoenix, AZ                  -112.08         33.42
             Pittsburg, PA                 -80.00         40.42
             Portland, OR                 -122.50         45.50
             Providence, RI                -76.42         41.92
             Rochester, NY                 -77.58         43.17
             Richmond, VA                  -77.42         37.58
             Riverside, CA                -117.33         34.00
             St. Louis, MO                 -90.17         38.62
             Sacramento, CA               -121.50         38.58
             Salt Lake City, UT           -112.00         40.75
             San Antonio, TX               -98.50         29.42
             San Diego, CA                -117.17         32.75
             San Francisco, CA            -122.42         37.75
             San Jose, CA                 -121.92         37.33
             San Pedro, CA                -118.31         33.74
   ASTROCLK Astronomical Clock and Celestial Tracking Program        Page 42


             CITY                       LONGITUDE      LATITUDE
             --------------------------------------------------
             Santa Monica, CA             -118.50         34.00
             Seattle, WA                  -122.33         47.67
             Springfield, MA               -72.58         42.08
             Toledo, OH                    -83.50         41.67
             Trenton, NJ                   -74.75         40.25
             Washington, DC (USNO)         -77.07         38.92
             Wilmington, DE                -75.50         39.75

             Calgary, Alberta             -114.00         51.00
             Edmonton, Alberta            -113.50         53.67
             Halifax, Nova Scotia          -63.58         44.67
             Hamilton, Ontario             -79.50         43.25
             Montreal, Quebec              -73.58         45.50
             Ottawa, Ontario               -75.67         45.42
             Quebec, Quebec                -71.17         46.87
             Regina, Saskatchewan         -104.50         50.50
             Toronto, Ontario              -79.33         43.67
             Vancouver, British Columbia  -123.08         49.25
             Winnipeg, Manitoba            -97.25         49.92

             An additional city file, USCITIES.CTY, is also available and 
        includes some 718 U. S. cities with greater accuracy than that 
        shown above. No Canadian cities are included in USCITIES.CTY.
   ASTROCLK Astronomical Clock and Celestial Tracking Program        Page 43



        SETTING LOCAL CONDITIONS

             ASTROCLK makes certain default assumptions about the current 
        conditions when computing horizon dip (a function of the 
        observer's elevation above mean sea level) and atmospheric 
        refraction. These calculations are used in the Horizon (Observer) 
        Coordinates data in Display Mode 0 and for certain navigation 
        calculations. The default values are:

                  Elevation:         0 meters/feet
                  Temperature:      20 degrees Centigrade
                                    68 degrees Farenheit
                  Pressure:       1010 millibars
                                 29.83 inches of Mercury

             If these default values are not representative of your 
        current conditions, use ALT-F6 to set the correct LOCAL 
        CONDITIONS. The following information will be displayed:

                  SET LOCAL CONDITIONS

                  Current ELEVATION:    152.4 m   =   500.0 ft
                  Current TEMPERATURE:   20.0  C  =    68.0  F
                  Current PRESSURE:      1010 mb  =    29.83" 

        The following prompts will be displayed to enable you to change 
        each item:

                  Enter ELEVATION (meters):
                  Enter TEMPERATURE ( C):
                  Enter PRESSURE (mb):

        For each item, press RETURN to leave that item unchanged or enter 
        the new information. Elevation assumes the entry in meters unless 
        you add the letter "F" to specify FEET, Pressure assumes degrees 
        Centigrage unless you add the letter "F" to specify degrees 
        Farenheit, and Pressure assumes millibars unless you enter a 
        number less than 32.00 or add the letters "IN". Note that in the 
        United States and for air traffic control, pressures are often 
        given in hundreths of an inch, as in "2983"; this must be entered 
        as "29.83".
             When all three items have been entered or accepted as is, 
        the following prompt will appear:

                  Press RETURN to ACCEPT, SPACE to REDO:      

        Press RETURN to accept the entries as shown, or press SPACE BAR 
        to start over.
             Since the elevation of a geographic location will probably 
        remain constant with time, absent some major disturbance, that 
        value is saved in the file ASTROCLK.INI and is restored each time 
        ASTROCLK is restarted. However, the values for temperature and 
        pressure, being quite variable, are not saved and are restored to 
        their default values each time ASTROCLK is restarted.
   ASTROCLK Astronomical Clock and Celestial Tracking Program        Page 44



        DUAL-TIME DISPLAYS

             A Dual-Time display feature is available which displays two 
        different, selectable times in large characters in the main 
        display window. Display Modes 1 through 5 normally display the 
        following times in large characters in the main screen window:

                  1    Local Standard/Daylight Time
                  2    Universal Coordinated Time
                  3    Local Mean Sidereal Time
                  4    Greenwich Mean Sidereal Time
                  5    Terrestrial Dynamical Time
                       (Ephemeris Time prior to 1984)

             Display Mode 1, Local Standard/Daylight Time, is the display 
        mode which appears when program ASTROCLK is started. The large 
        digit time display modes may be selected at any time by pressing 
        the number keys 1 through 5. Use the number keys at the top of 
        the keyboard and NOT the number keys on the numeric keypad. The 
        title at the top of the main window gives the standard 
        abbreviation and full name of the time displayed.
             To enable a dual-time display, select one of the clock 
        display modes using the number keys 1 through 5, and then press 
        the UP or DOWN arrow key. The normally displayed time will move 
        up in the window and a second time will appear in yellow in the 
        lower half of the window. Repeated pressing of the UP or DOWN 
        arrow key will cycle through the following lower clock displays:

                  PST/PDT   Pacific Standard/Daylight Time
                  MST/MDT   Mountain Standard/Daylight Time
                  CST/CDT   Central Standard/Daylight Time
                  EST/EDT   Eastern Standard/Daylight Time
                  TAI/A.1   International Atomic Time (after 1971)
                            USNO Atomic Time (1958 through 1971)
               5  TDT/ET    Terrestrial Dynamical Time (after 1983)
                            Ephemeris Time (prior to 1984)
               4  GMST      Greenwich Mean Sidereal Time
               3  LMST      Local Mean Sidereal Time
               2  UTC       Universal Coordinated Time
               1  LST       Local STANDARD/DAYLIGHT Time (Mode 1 only)
                            Local STANDARD Time (Modes 2 thru 5)

             The UP arrow key cycles UP through the list above starting 
        with the normal time for that display mode as indicated by the 
        numbers at the left; the DOWN arrow key cycles DOWN through the 
        list. Each display may be returned to the normal, single-time 
        mode by pressing the HOME key. Note that the first five times 
        listed can ONLY be displayed in large digits by using the DUAL 
        TIME method.
             The first four times are for the standard time zones in the 
        continental United States and will display Standard or Daylight 
        time in agreement with the current setting of the Daylight Flag 
        (ALT-F10). If the local time is a continental U. S. time zone, it 
        is possible to display the same time in both the upper and lower 
   ASTROCLK Astronomical Clock and Celestial Tracking Program        Page 45


        portion of the window in Display Mode 1. These times are 
        calculated independently of the current local time zone.
             When the dual-time display is enabled, the abbreviation 
        corresponding to the time displayed will also appear at the right 
        of the time digits for each clock. For time zones in the United 
        States, the abbreviation will change from LST (Local Standard Time) 
        to the common U. S. abbreviation: PST for Pacific Standard Time, 
        EST for Eastern Standard Time, HST for Hawaiian Standard Time, 
        etc. The single or dual time selected for each of the five 
        display modes is saved while ASTROCLK is running; changing to a 
        different Display Mode and back again will display the same 
        time(s). The single or dual time selected for each mode is also 
        saved in file ASTROCLK.INI and will be restored when ASTROCLK is 
        run the next time.
             Note that the Local STANDARD Time can be selected for the 
        lower clock in Display Modes 2 through 5, whether or not the 
        DAYLIGHT FLAG has been set. During daylight time, therefore, this 
        display will show a different time from the small LOCAL TIME 
        display on the right of the screen. Since some references and 
        magazines give all times in standard time, this display will 
        eliminate having to make the conversion if you are on daylight 
        time.
             If the date has been set for 1958 through 1971, U.S. Naval 
        Observatory Atomic Time (USNO A.1) is displayed instead of 
        International Atomic Time (TAI). If the date has been set prior 
        to 1958, a message in the lower portion of the window will remind 
        the user that TAI and A.1 did not exist on the selected date. 
        There is a slight (0.034 seconds) difference in the relationship 
        of the two atomic time scales to TDT/ET.
             If the date has been set prior to 1984, Ephemeris Time (ET) 
        is displayed instead of Terrestrial Dynamical Time (TDT). For 
        most purposes, TDT and ET represent a continuous time scale and 
        are treated as such by ASTROCLK; the only difference is the name 
        displayed. 
             There are, of course, many combinations possible. For 
        example, you can display UTC and Local STANDARD Time, UTC and 
        GMST, GMST and LMST, TDT and TAI, and so forth. If you are about 
        to call the East from Los Angeles, you can display both Eastern 
        and Pacific times, Standard or Daylight depending on the current 
        setting of the Daylight Flag. Each of the five display modes is 
        independent of the other four, and may be set up to display 
        either its normal time alone, or dual time with one of the other 
        remaining times.
   ASTROCLK Astronomical Clock and Celestial Tracking Program        Page 46



        ALARM AND INTERVAL TIMER OPERATIONS

             ASTROCLK includes alarm and interval timer functions which 
        operate independently of the program's clock modes. That is, the 
        alarm and interval timer ALWAYS use the computer's internal clock 
        for their operations, even with the ASTROCLK clocks off or in the 
        simulation mode. The correct alarm and interval times, referenced 
        to the computer's internal clock (Local Time), are therefore 
        displayed in all clock modes. The interval timer window is 
        displayed at all times at the lower center of the screen, but the 
        alarm window is only displayed at the lower right of the screen 
        when an alarm is active.


        Using the ALARM Function

             The alarm function allows the user to set an alarm to any 
        time within the next 23 hours using either Local or UT Time. When 
        an alarm is active, the program opens a small Alarm Window at the 
        lower right corner of the display screen which displays the 
        selected alarm time in the left side of the window and the 
        coundown time, or time remaining until the alarm, in the right 
        side of the window. The color of the countdown time changes as 
        the local time approaches the selected time, from gray to white 
        to yellow to blinking yellow.
             To set or change the alarm time, press Function Key SHIFT-F3 
        and enter the desired Local or UT Time in the format HH:MM:SS, 
        HH:MM or HH.HHH, using the same flexible format rules as for 
        setting the program time. If you prefer, use the comma instead of 
        the colon for the separator between units. Add the letter "U" if 
        the alarm time you are entering is UT Time; ASTROCLK will 
        automatically convert the UT Time to Local Time and the Local 
        Time will be displayed in the Alarm Window. If an alarm time has 
        already been set and you wish to clear it, press SHIFT-F3 and 
        then simply press RETURN instead of entering a time.
             Once an alarm time has been set using Function Key SHIFT-F3, 
        the alarm countdown time (the time remaining until the selected 
        alarm time is reached) may also be displayed in the main display 
        window by pressing the letter "A" on the keyboard. The small 
        window at the lower right of the display screen will still show 
        both the selected alarm time and the countdown time. If no alarm 
        time has been set, pressing the letter "A" will have no effect. 
        The alarm function remembers the prior main window display 
        function; if the alarm countdown time is displayed in the main 
        display window when the alarm time is reached, the main display 
        will automatically revert to the prior function. As further 
        described below, the interval timer can also be synchronized to 
        the time an alarm occurs.


   ASTROCLK Astronomical Clock and Celestial Tracking Program        Page 47


        Using the INTERVAL TIMER

             ASTROCLK includes an interval timer function, measuring 
        elapsed time rounded to the nearest second. The current value of 
        the interval timer is always shown in the TIMER window at the 
        lower center of the display in the format 00  00:00:00, 
        corresponding to days and hours:minutes:seconds. The TIMER window 
        allows times from +9999 days to -999 days; the days portion will 
        be blanked if the day count falls outside this range. When the 
        Interval Timer is displayed in the main display window using the 
        "T" command, the range for that display is from +999 days to -99 
        days; the main window display should not be used outside this 
        range as the interval time will NOT be updated. The interval 
        timer display in the TIMER window is white (gray) when the timer 
        is OFF, and yellow when the timer is ON.
             The following keys are used to control the operation of the 
        interval timer:

                  T    Display interval timer in main display window
                  S    Start/Stop the interval timer without reset
                  Z    Stop and reset the interval timer
                  PgUp Increment the interval timer DAYS
                  PgDn Decrement the interval timer DAYS

                  NOTE: The PgUp and PgDn keys are only active when the 
                  interval timer is displayed in the main display window 
                  using the "T" command.

             The interval timer may be started by one of three methods: 
        manually, by pressing the letter "S"; automatically, when an 
        alarm time occurs AND the interval timer is not already ON; or by 
        setting the interval timer starting time with Function Key SHIFT-
        F3. When the interval timer is started automatically or by 
        setting its starting time, it starts at zero. Note that the 
        interval timer will NOT be automatically reset and started by the 
        alarm function if it is already ON; in this case the interval 
        timer will be unaffected by alarm operations.
             The interval timer starting time may be set using Function 
        Key SHIFT-F3. Enter the desired starting time followed by the 
        letter "T". If the entered time is later than the current time, 
        ASTROCLK assumes the prior day. The total elapsed time will 
        therefore always be less than 24 hours. To adjust the starting 
        DAY, set the desired starting time, display the interval timer in 
        the main display window using the "T" command, then use the PgUp 
        and PgDn keys to set the days.
             Press the letter "S" to start or stop (but not reset) the 
        interval timer. The timer may be stopped and started as often as 
        desired whether or not the interval timer is displayed in the 
        main display window. Press the letter "Z" to stop the interval 
        timer and reset the accumulated time to zero. When the interval 
        timer is displayed in the main display window and the timer is 
        stopped, the words "TIMER IS HOLDING" will flash at the bottom of 
        the window.
             The status of the interval timer is saved when ASTROCLK is 
        halted. If the interval timer is active when the program is 
   ASTROCLK Astronomical Clock and Celestial Tracking Program        Page 48


        halted, it will resume operation when next the program is started 
        and the correct elapsed time interval (including days) will be 
        displayed. If the interval timer is stopped but not reset when 
        ASTROCLK is halted, the current elapsed time will be restored and 
        the interval timer will be stopped when next the program is 
        started.


        Linked ALARM & INTERVAL TIMER Operation

             If the interval timer is stopped and reset when the alarm 
        time occurs, the interval timer will auotmatically start at the 
        alarm time. The alarm and the interval timer then function 
        together as a count-down-then-count-up timer. A typical operation 
        in this manner may best be illustrated by an example. I used this 
        arrangement during the launch of the Space Shuttle DISCOVERY on 
        September 29, 1988 and throughout the four day mission. I first 
        checked the system clock using radio station WWV from the 
        National Bureau of Standards. 
             To set up ASTROCLK correctly, I pressed "Z" to stop and 
        reset the interval timer (if it did not display 00 00:00:00), 
        next entered the scheduled lift-off time on the alarm using 
        Function Key SHIFT-F3, then pressed the letter "T" to display the 
        interval timer (to establish the "prior display mode" for the 
        alarm function), followed by the letter "A" to display the alarm 
        countdown time. ASTROCLK displayed the countdown time until lift-
        off and then automatically switched the main display to the 
        interval timer to show Mission Elapsed Time (MET) throughout the 
        four day mission. The main display may be switched to other 
        display functions without affecting the accuracy of the countdown 
        or elapsed times. Once the interval timer has started, ASTROCLK 
        may be halted and restarted and the time will be preserved. Since 
        the interval timer can continue for up to 9999 days, any mission 
        or other event of reasonable duration can easily be handled.
   ASTROCLK Astronomical Clock and Celestial Tracking Program        Page 49



        TARGET TRACKING DISPLAY

             One of the problems that inspired program ASTROCLK in the 
        first place was my inability to figure out where a star or planet 
        could be located in the night sky even if I knew its equatorial 
        coordinates, the right ascension and declination. These 
        coordinates have to be converted to horizon coordinates, also 
        known as observer coordinates, in order to relate the position of 
        a star with my own position and the time. (Of course, I had to 
        know the direction of true North as well, but even I could 
        usually find Polaris without excessive difficulty.)
             Display Mode 0, the Target Tracking Display, provides this 
        information in real time for both stars and planets -- although 
        there are significant computational delays associated with the 
        planetary positions if the micro-computer does not have a math 
        coprocessor. The default target is Polaris, the North Star, which 
        I have assigned the number zero in ASTROCLK's internal star 
        database. Use Function Key F5 to select other celestial objects 
        for tracking. Pressing "P" while in the Target Tracking Display 
        will request the planet to track and then automatically calculate 
        and display the position data for the planet.
             When already in Display Mode 0, the Target Tracking Display, 
        pressing the "0" key again toggles between the full display (as 
        described in the following paragraphs) and a large digit display 
        showing the Horizon Coordinates for the target, with the APPARENT 
        ALTITUDE on the top line and the AZIMUTH on the bottom line. The 
        format will change with Function Key F7 (see below). However, the 
        precision of the large digit display is two digits fewer than the 
        full (text) display due to restricted display space.
             The following sample display shows the information available 
        in the Target Tracking Display. The degree symbol, which appears 
        in the actual display, has been deleted from the sample because 
        of the differences among printers.

        0 - a Ursae Minoris - Polaris
        -----------------------------

             EQUATORIAL COORDINATES [J2000.0]:
               RIGHT ASCENSION:                 2:31:48.70 
               DECLINATION:                    89 15'50.72"
               HOUR ANGLE (hours):             17:07:49.20 
             APPARENT COORDINATES [J1988.9]:
               RIGHT ASCENSION:                 2:20:08.44 
               DECLINATION:                    89 12'51.34"
               HOUR ANGLE (hours):             17:19:29.45 
             OBSERVER HORIZON COORDINATES:
               ALTITUDE:                       33 37'33.09"
               AZIMUTH (NESW):                  0 55'44.18"
               Apparent ALTITUDE:              33 38'57.11"
             [Charts SA=1 U=I-1]             [VMag =  2.02]

             The Equatorial Coordinates are first shown for the current 
        epoch of the internal star database; the default is J2000.0, as 
        shown in the sample above. These data are "mean" positions for 
   ASTROCLK Astronomical Clock and Celestial Tracking Program        Page 50


        the epoch shown, as found in typical star catalogs.
             The Apparent Coordinates are the apparent geocentric 
        equatorial coordinates which have been (for stars) precessed and 
        corrected for proper motion, nutation, and annual aberration but 
        NOT parallax, or (for planets) calculated as of the mean equinox 
        of date, J1988.9 in the sample. The stellar apparent geocentric 
        equatorial coordinates agree with the Astronomical Almanac and 
        the USNO Interactive Computer Ephemeris to an accuracy of 
        typically less than one second of time or arc; planetary data are 
        less accurate.
             Versions of ASTROCLK prior to 8847 displayed "apparent 
        coordinates" which were the current star database coordinates 
        adjusted for refraction. The present display is in keeping with 
        the accepted definition of "apparent" (that is, referenced to the 
        mean equinox of date), and the coordinates have NOT been 
        corrected for refraction.
             The local HA (Hour Angle, hours) is related to the RA (Right 
        Ascension, hours) and LMST (Local Mean Sidereal Time, hours) by 
        the formula:

                  HA = LMST - RA

        Technically, the LAST Local Apparent Sidereal Time should be 
        used, but I have compromised, as have some of my sources, since 
        the difference is small (on the order of 0.2 seconds in 1988) and 
        many calculations can thereby be avoided; while not particularly 
        important if your computer has a math coprocessor, the delay may 
        be significant if it does not.
             The Horizon (or Observer) Coordinates are referenced to the 
        current ASTROCLK local geographical coordinates. The Altitude is 
        the angle above the true horizon, and the Azimuth is the angle 
        from true North, measured in the sense NESW. Thus, North is 0 
        degrees, East is 90 degrees, South is 180 degrees, and West is 
        270 degrees. The Apparent Altitude is the Altitude corrected for 
        atmospheric refraction and horizon dip (if the local elevation is 
        non-zero); Azimuth is unaffected by refraction.
             The approximate visual or photographic magnitude of the 
        object is shown at the lower right of the window border, marked 
        as "VMAG" (visual magnitude) for stars and planets or "BMAG" 
        (blue/photographic magnitude) for minor planets. The values for 
        stars are constant values from the internal or external catalog 
        while those for planets and minor planets are calculated 
        approximations for the current time and date.
             The chart numbers in two of the most commonly used star 
        atlases are shown for the target object in the Chart data at the 
        lower left of the target window. "SA=" gives the chart number in 
        Sky Atlas 2000.0 and "U=" gives the volume(s) and chart number 
        for Uranometria 2000.0. Of course, the target object may or may 
        not appear on the chart, depending upon the type of object and 
        its magnitude; planets, for example, will not appear because of 
        their constantly changing positions. Even when the object does 
        not appear on the chart, however, the chart for the proper area 
        may be useful to establish neighboring stars, the constellation 
        name, etc. The original algorithm used to calculate the chart 
        numbers was published in Sky & Telescope Magazine in April 1989; 
   ASTROCLK Astronomical Clock and Celestial Tracking Program        Page 51


        the algorithm has been substantially modified and converted to 
        QuickBASIC for use in ASTROCLK.
             Function Key ALT-F7 changes some of the units used for the 
        Target Tracking Display, as shown in the following sample (and 
        again, the degree symbol has been deleted).

        0 - a Ursae Minoris - Polaris
        -----------------------------

             EQUATORIAL COORDINATES [J2000.0]:
               SIDEREAL HR ANGLE   [SHA]:     322 02'49.43"
               DECLINATION         [DEC]:      89 15'50.72"
               GREENWICH HR ANGLE  [GHA]:      15 21'29.95"
             APPARENT COORDINATES [J1988.9]:
               SIDEREAL HR ANGLE   [SHA]:     324 57'53.18"
               DECLINATION         [DEC]:      89 12'51.34"
               GREENWICH HR ANGLE  [GHA]:      18 16'33.70"
             OBSERVER HORIZON COORDINATES:
               ALTITUDE            [Hc]:       33 37'33.09"
               AZIMUTH (NESW)      [Zn]:        0 55'44.18"
               Apparent ALTITUDE   [Ho]:       33 38'57.11"
             [Chart SA=1 U=I-1]              [VMag =  2.02]

             This alternate form of the Target Tracking Display shows the 
        same basic information as above, but in a form preferred by 
        navigators. Press ALT-F7 again to return to the original format. 
        SHA (Sidereal Hour Angle, degrees) is related to RA (Right 
        Ascension, hours) by the formula:

                  SHA = 360 - RA * 15

        GHA (Greenwich Hour Angle, degrees) is related to SHA (Sidereal 
        Hour Angle, degrees) and GAST (Greenwich Apparent Sidereal Time, 
        hours) by the formula:

                  GHA = 15 * GAST + SHA

        Not shown but also occasionally required is LHA (Local Hour 
        Angle, degrees) which is obtained using the following formula:

                  LHA = GHA + Longitude

        The abbreviations shown in square brackets [...] are those given 
        in the Nautical Almanac and the USNO Almanac for Computers for 
        use in navigation.
             Note that in this mode, the Apparent Altitude will show the 
        abbreviation [Ho] if the local elevation is zero, and [Hs] if the 
        local elevation is non-zero. [Ho] refers to the "observed" 
        altitude after corrections for horizon dip and instrument error, 
        while [Hs] refers to the "sextant" altitude after correction for 
        instrument error but as measured to the actual horizon. If the 
        navigational instrument being used provides its own artificial 
        horizon, set the local elevation to zero.
             Function Key F7 may be used to change the units used in the 
        Target Tracking Display. Three different formats for time and 
   ASTROCLK Astronomical Clock and Celestial Tracking Program        Page 52


        degrees are available; press F7 to cycle through the formats:

                       ANGLES              TIME
                       ------------        -----------
                       DDD MM SS.SS        HH:MM:SS.SS
                       DDD MM.MMMM         HH:MM.MMMM
                       DDD.DDDDDD          HH.HHHHHH

        However, note that the large digit display (showing Apparent 
        Altitude and Azimuth) and obtained by pressing the "0" key when 
        in the Tracking Data Mode, displays the data to lower precision 
        due to screen space restrictions.
   ASTROCLK Astronomical Clock and Celestial Tracking Program        Page 53



        TARGET OBJECT EPHEMERIS

             Quite a number of ASTROCLK users have requested the 
        capability of displaying and/or printing an ephemeris, a listing 
        of the position of a celestial object for a series of specific 
        dates and times. While ASTROCLK was intended more as a real time 
        clock and tracking program than for the generation of tabular 
        data, it is admittedly very useful to be able to produce such a 
        listing in anticipation of an evening with behind your telescope. 
        Because of increasingly severe memory constraints, direct 
        printing is not possible with this version of ASTROCLK except by 
        using the SHIFT-PrtSc key. However, Function Key F2 now displays 
        an ephemeris for the current target object, replacing the 
        previous function of cycling through the various clock displays.
             Before pressing Function Key F2, ASTROCLK must be set up for 
        the desired target object (star, planet, minor planet, etc.) 
        using Function Key F5. For most objects outside the solar system, 
        of course, the position will change very slowly with time. Next 
        set the desired starting time using Function Key F3. Two 
        additional items are required before the ephemeris can be 
        displayed, the step interval (the time from one calculation to 
        the next) and the number of intervals.

                  SET TARGET EPHEMERIS PARAMETERS

                  The ephemeris will be generated for the current
                  TIME and DATE. Use F3 to change.

                  Enter INTERVAL [1 day]:

                  Enter the ephemeris step interval in DAYS, or: 
                    Add 'Y' or 'y' for 365-day YEARS.
                    Add 'H' or 'h' for HOURS.
                    Add 'M' or 'm' for MINUTES.

             The default units for the interval are DAYS; simply enter 
        the number of days between steps and press RETURN. If you wish 
        other units, 365-day years, hours, or minutes, add the letter Y, 
        H, or M (upper or lower case) respectively following the number.

                  Enter number of intervals [10]:

        Then enter the total number of intervals desired or press RETURN 
        for 10 intervals. ASTROCLK will generate the ephemeris with 20 
        lines per display screen. When the complete ephemeris has been 
        displayed and each time the screen fills, the program will pause 
        so that you may read or print the information. Press any key to 
        continue. After the ephemeris is completed, ASTROCLK will resume 
        normal operation.
             The following is a sample ephemeris generated for the planet 
        Neptune on August 30, 1989 with an interval set to one day and 
        ten intervals requested:

   ASTROCLK Astronomical Clock and Celestial Tracking Program        Page 54


               ASTROCLK EPHEMERIS FOR: Planet #8  NEPTUNE (Automatic)
                                               Equinox of Date [J1989.6]
           Julian Date  Local Date  PDT Time   Rt. Ascen.    Declination
        2447769.478183  30-08-1989  16:28:35  18:42:04.82  -22 10'38.63"
        2447770.478183  31-08-1989  16:28:35  18:42:02.00  -22 10'43.65"
        2447771.478183  01-09-1989  16:28:35  18:41:59.31  -22 10'48.61"
        2447772.478183  02-09-1989  16:28:35  18:41:56.75  -22 10'53.43"
        2447773.478183  03-09-1989  16:28:35  18:41:54.31  -22 10'58.11"
        2447774.478183  04-09-1989  16:28:35  18:41:52.00  -22 11'02.67"
        2447775.478183  05-09-1989  16:28:35  18:41:49.83  -22 11'07.07"
        2447776.478183  06-09-1989  16:28:35  18:41:47.79  -22 11'11.35"
        2447777.478183  07-09-1989  16:28:35  18:41:45.90  -22 11'15.52"
        2447778.478183  08-09-1989  16:28:35  18:41:44.13  -22 11'19.54"

        As usual in these text examples, the degree symbol has been 
        omitted because of printer differences, and the right-most 
        column, giving the object's magnitude, has been deleted because 
        of space limitations; the value was 7.89 and 7.90 for the dates 
        shown. The Local Date and Time are based upon the current 
        geographical coordinates and time corrections (DAYLIGHT FLAG and 
        ZONE CORRECTION); the time zone abbreviation, PDT in the example, 
        is also included. Note that the coordinates shown are the 
        Apparent Geocentric Equatorial Coordinates for the Epoch and 
        Equinox of Date, J1989.6 in the example.
   ASTROCLK Astronomical Clock and Celestial Tracking Program        Page 55



        PRECISION TIME AND DATA DISPLAYS

             The ASTROCLK on-screen clocks on the right portion of the 
        screen display times rounded the nearest second. It is sometimes 
        useful to view the various times and other parameters to a higher 
        precision. Display Mode 8 provides this facility with five 
        precision displays: two Precision Time Displays and three 
        Precision Data Displays. Switch between the displays with the 
        PgUp or PgDn keys, or press the "8" key. When ASTROCLK exits, the 
        current Precision Time/Data Display window is saved; that window 
        will appear when Display Mode 8 is next selected.
             When ASTROCLK is first executed, this mode shows Precision 
        Time Display #1 with all times shown to a precision of 0.0001 
        seconds. Note, however, that the displayed precision may be 
        greater than the accuracy of the calculations as discussed below.
             The limitations of a microcomputer and the available 
        software become apparent as more complex calculations are 
        attempted. Given unlimited execution time and appropriate 
        software, of course, there is no reason why the microcomputer 
        cannot produce data to any desired accuracy. However, the real 
        world imposes certain constraints and the complex mathematics of 
        practical astronomy forces compromises. Even with a math 
        coprocessor, the calculation times are noticeable; without the 
        math coprocessor they are significant.
             The Precision Data Displays show various intermediate 
        parameters required for the calculation of some of the basic 
        astronomical quantities. Each is an important item in its own 
        right, but in the context of a program such as ASTROCLK, its 
        function is more nearly that of the building block needed to 
        construct the whole. Readers are again reminded that the 
        precision of the displayed data is generally greater than its 
        accuracy; the higher precision has been retained as a testing 
        tool as the program's accuracy is gradually increased through 
        improved algorithms and technique.
             The sample displays were all generated at 00:00:00 UT for 
        4 November 1988. The Daylight Flag was OFF and the Local 
        Coordinates were set for Calaveras County, near Sacramento, in 
        Northern California (preset location "CAL").
             As an additional feature, the UP and DOWN arrow keys may be 
        used to increase or decrease the Julian Date by one day when 
        using the precision displays in Display Mode 8, but ONLY when the 
        clocks are OFF; use Function Key F4 to start and stop the 
        clocks. The UT time remains constant, but all other data are 
        recalculated. I have used this feature while comparing the 
        ASTROCLK calculations against tabulated data; how useful it may 
        otherwise be is questionable.

        Precision Time Display #1:
        --------------------------

           UTC Coordinated Universal Time:  0:00:00.2404
            UT Universal Time (=UT1):       0:00:00.0000
           TAI International Atomic Time:   0:00:24.2404
           TDT Terrestrial Dynamical Time:  0:00:56.4244
   ASTROCLK Astronomical Clock and Celestial Tracking Program        Page 56


               Gwich Mean Solar Time (UT):  0:00:00.0000
               Greenwich App. Solar Time:   0:16:24.2747
          GMST Grnwich Mean Sidereal Time:  2:57:45.7030
          GAST Grnwich App. Sidereal Time:  2:57:45.9618

           GSD Greenwich Sidereal Date:   2454172.123446

        NOTES: For the period 1958 through 1971, A.1 USNO Atomic Time 
        will be shown in place of TAI International Time. Prior to 1984, 
        ET Ephemeris Time will be shown in place of TDT Terrestrial 
        Dynamical Time.

             The basic time reference for all internal ASTROCLK time 
        calculations is Universal Time (UT), whether derived from the 
        computer's internal clock or entered manually. This time is 
        therefore considered to be exact and accurate to the full 
        precision shown and is the same as UT1.
             Universal Coordinated Time (UTC), which is the time 
        broadcast by radio stations WWV, WWVH, and most other radio time 
        standards, is kept to within 0.9 seconds of UT by the occasional 
        insertion of Leap Seconds at the end of June or December. Except 
        for this Precision Time Display, which shows the calculated or 
        estimated difference between UT and UTC, ASTROCLK otherwise 
        assumes UT for all time calculations.
             International Atomic Time (TAI) has been officially 
        recognized as an official time standard since 1972 although 
        the U.S. Naval Observatory has provided an atomic time standard 
        since 1958. The difference between TAI and UTC is published in 
        the Astronomical Almanac for years 1972 and up. For the period 
        1958 through 1971, ASTROCLK calculates USNO Atomic Time (A.1). 
        The difference between A.1 and UTC ranges from 0 to 10 seconds 
        and ASTROCLK assumes a linear rate of change with one second 
        increments added on January 1 or July 1 when appropriate. The 
        offset between TAI and A.1 versus TDT/ET is slightly different: 
        32.184 seconds versus 32.15 seconds respectively. Prior to 1958, 
        ASTROCLK does not display an atomic time.
             Terrestrial Dynamical Time (TDT) and its pre-1984 cousin 
        Ephemeris Time (ET) are calculated for the period 1620 through 
        1989 based upon data published in the Astronomical Almanac. 
        Outside that period a formula by Meeus, adjusted slightly to 
        merge smoothly with the data in the Astronomical Almanac, has 
        been used (see BIBLIOGRAPHY). The Astronomical Almanac advises 
        that for most purposes ET and TDT may be considered a continuous 
        time standard. ASTROCLK uses the appropriate designation, ET or 
        TDT, depending upon the current date but otherwise makes no 
        distinction between them. Terrestrial Barycentric Time (TBT) is 
        never more than 1.7 milliseconds different from TDT and is not 
        shown; for most calculations the two may be considered the same.
             ASTROCLK's calculation of Greenwich Mean Sidereal Time 
        (GMST) has been compared with the published Astronomical Almanac 
        data for the year 1988 and agrees to the full precision shown, 
        0.0001 seconds. However, Greenwich Apparent Sidereal Time (GAST) 
        involves many more calculations and the accuracy falls off to 
        approximately 0.01 seconds.

   ASTROCLK Astronomical Clock and Celestial Tracking Program        Page 57


        Precision Time Display #2:
        --------------------------

           PST Local Standard Time:        16:00:00.0000
               Local Mean Solar Time:      15:57:43.9999
               Local App. Solar Time:      16:14:08.2747
          LMST Local Mean Sidereal Time:   18:55:29.7029
          LAST Local App. Sidereal Time:   18:55:29.9617

               Equation of Time:          + 0:16:24.2747
               Delta T  (TDT/ET-UT):        0:00:56.4244
               Delta AT (TAI-UT):           0:00:24.0000

             For locations within the United States as well as for other 
        areas falling in the same time zones, the abbreviation PST will 
        be replaced by the abbreviation appropriate for the local time 
        zone. In addition, the middle letter will change (S or D) 
        depending upon whether Standard or Daylight time is in effect, as 
        determined by the setting of the Daylight Flag. For other time 
        zones, the abbreviation PST will be replaced by LST (Local 
        Standard Time) or LDT (Local Daylight Time) according to the 
        setting of the Daylight Flag.
             The local times shown have essentially the same accuracy as 
        the corresponding Universal or Sidereal times (given upon the 
        assumption that the local coordinates are exact). Thus, Local 
        Standard/Daylight Time may be considered exact (provided the 
        Daylight Flag and Zone Correction have been correctly set), Local 
        Mean Sidereal Time is accurate to the precision shown, and Local 
        Apparent Sidereal Time is accurate to approximately 0.01 seconds. 
        Local Mean Solar Time, calculated using UT and the local 
        longitude, is accurate to approximately the precision shown.
             The Equation of Time is the difference between the Right 
        Ascension of the apparent Sun and the fictitious mean Sun. In 
        addition to being required for various calculations, it 
        represents the difference between mean solar time (upon which our 
        civil timekeeping is based) and apparent solar time, the time 
        shown by a sundial.
             Delta T and Delta AT show the calculated or estimated 
        difference between UTC versus TDT/ET and TAI/A.1 respectively. 
        Prior to 1958, Delta AT is not shown. In ancient times, Delta T 
        can reach values greater than 24 hours; in this case, Delta T is 
        shown as days (suffixed by "d") followed by hours as usual. The 
        error in Delta T for ancient times is estimated to be as much as 
        several hours.

        Precision Data Display #1:
        --------------------------

                Mean Obliquity of Ecliptic:   23 26'26.63"   [0.02"]
                True Obliquity of Ecliptic:   23 26'35.40"   [0.02"]
                Nutation in Longitude:         0 00'04.32"   [0.05"]
                Nutation in Obliquity:         0 00'08.76"   [0.05"]
                Equation of Equinoxes (secs):  0.263960      [0.005 sec]
             e  EARTH Eccentricity of Orbit:   0.01671380  
             L' MOON Mean Longitude:         157 55'15.39" 
   ASTROCLK Astronomical Clock and Celestial Tracking Program        Page 58


             M' MOON Mean Anomaly:           168 35'33.91" 
                MOON Asc Node Longitude:     340 51'23.71" 
             E  Equation of Time (h:m:s):    + 0:16:25.8574
             T  Jul Cent @ 2000 JAN 1.5 TDT:  -0.111581091 
                         @ 1900 JAN 0.5 ET:    0.888418909 

        NOTES: All items are expressed in degrees or time as appropriate, 
        with the format determined by Function Key F7. In the actual 
        ASTROCLK display, the last parameter is shown with the omega 
        symbol usually associated with that parameter, and all items in 
        degrees include the degree symbol. Because of the differences 
        among printers, those symbols have been omitted in this text.

             The numbers in the right hand column above are the 
        approximate accuracy of the calculations compared with data 
        published in the Astronomical Almanac. Items with no accuracy 
        data shown have been checked against other sources and appear to 
        be accurate to about 0.001 degrees or 0.1 seconds or better; the 
        MOON paramaters are used in the calculation of the first four 
        items of the precision times and therefore probably have at least 
        comparable accuracy. Function Key F7 may be used to change the 
        format of the displayed data as in other display modes. In the 
        default mode (degrees or hours, minutes, and seconds), data are 
        displayed to a precision of 0.01 seconds of arc or time.

        Precision Data Display #2:
        --------------------------

             Geocentric Data @ Equator & Ecliptic of Date:
             ---------------------------------------------
             L  SUN Mean Longitude:          223 27'38.75"
             0  SUN True Longitude:          221 47'42.02"
             0a SUN Apparent Longitude:      221 47'27.20"
             M  SUN Mean Anomaly:            300 42'43.97"
             v  SUN True Anomaly:            299 02'53.02"
             R  SUN Radius Vector (AU):        0.99167759 
             C  SUN Equation of Center:       -1 39'50.95"
             a  SUN Apparent Rt. Ascension:   14:37:24.72 
             d  SUN Apparent Declination:    -15 22'27.89"

        NOTES: All items are expressed in degrees or time as appropriate, 
        with the format determined by Function Key F7. In the actual 
        ASTROCLK display, Right Ascension and Declination are shown with 
        the alpha and delta symbols usually associated with those 
        parameters, and all items in degrees include the degree symbol. 

             This display shows the calculated values for parameters 
        associated with the Sun. CAUTION: Depending upon the source, 
        formulae used to calculate these and other precision data may 
        refer T to 2000 JAN 1.5 TDT, the new standard epoch, OR to 1900 
        JAN 0.5 ET, the prior standard epoch.

   ASTROCLK Astronomical Clock and Celestial Tracking Program        Page 59


        Precision Data Display #3:
        --------------------------

        SUN Geocentric Rectangular Equatorial Coords
        --------------------------------------------

        @ Mean Equator & Equinox of Date:           
              X Coordinate:               -0.7393294
              Y Coordinate:               -0.6063765
              Z Coordinate:               -0.2629145
        @ Mean Equator & Equinox of J2000.0:        
              X Coordinate:               -0.7375287
              Y Coordinate:               -0.6082189
              Z Coordinate:               -0.2637152

             The standard equator and equinox shown in the sample is 
        J2000.0, and is always the same as that used for the internal 
        star database. It may be set with Function Key F8 to any desired 
        epoch using a variety of input formats. These coordinates are 
        frequently required for Epoch B1950.0 for use with planetary and 
        other solar system data. NASA also uses B1950.0 for most data.
   ASTROCLK Astronomical Clock and Celestial Tracking Program        Page 60



        PLANETARY DATA DISPLAYS

             By far the most demanding task that ASTROCLK asks of the 
        micro-computer is the calculation of the positions of the 
        planets; it is also one of the more important tasks for the 
        interested star gazer, since the planets are among the more 
        distinctive objects easily seen with the naked eye. Beginning 
        with Version 8846, ASTROCLK calculates the full planetary 
        position at the current time (ecliptic and equinox of date), 
        displays its results using Display Mode 9, and makes those 
        results available to the Tracking Display, Display Mode 0. For a 
        micro-computer without a math coprocessor, the computational 
        delays are very significant; my Zenith Z-183, running at 8 Mhz, 
        requires about four to six seconds per position calculation, 
        depending upon the planet. For a micro-computer equipped with a 
        math coprocessor, the delays are noticeable but my Zenith Z-248 
        IBM AT-compatible gets the job done in less than one second.
             When the letter "P" is pressed, or the first time Display 
        Mode 9 is requested, ASTROCLK asks you to select a planet or 
        minor planet for display. The major planets are assigned their 
        "standard" numbers corresponding to their position outward from 
        the Sun. Planet #3, the Earth, cannot be selected. A planet may 
        be selected by entering either the planet number or the planet 
        name. Except for Mercury and Mars, the first letter (upper or 
        lower case) of the planet name is sufficient to select the 
        planet; the first two letters are required to distinguish between 
        MErcury and MArs. The letter "H" will select Comet Halley, the 
        letter "X" will select the external Minor Planet Catalog (if 
        present), and the letter "Z" allows manual entry of all orbital 
        parameters. See the section MINOR PLANET SELECTION for additional 
        information on minor planets and orbital parameters. The Planet 
        Selection display reminds the user of the planet's numbers and 
        names:

        PLANET SELECTION
        ----------------

                  Enter PLANET NAME/NUMBER:                   
                       1 = Mercury      6 = Saturn             
                       2 = Venus        7 = Uranus             
                       4 = Mars         8 = Neptune            
                       5 = Jupiter      9 = Pluto              
                       H = Comet Halley (internal data)        
                       X = External Minor Planet Catalog       
                       Z = Enter Orbital Parameters                                            
                  - All orbital elements @ Mean Equinox of Date
                  - Use UP and DOWN arrows to change PLANET    
                    after making initial selection.            

             Once the initial selection has been made or at any time from 
        another display mode, pressing "P" will allow you to select a 
        planet or minor planet and will automatically select Display Mode 
        9 unless you are in the Tracking Display, Display Mode 0. While 
        displaying planetary data in Display Mode 9, pressing the UP 
   ASTROCLK Astronomical Clock and Celestial Tracking Program        Page 61


        arrow will cycle through the planets (but not the minor planets!) 
        moving outward from the Sun and pressing the DOWN arrow will 
        cycle through the planets moving inward toward the Sun.
             The position of the selected planet is calculated in several 
        stages using the current time. First, current position data for 
        the Sun are calculated (as in the Precision Data Display), then 
        the orbital elements for all planets are determined for the 
        instant of interest. Next, the heliocentric (Sun-centered) and 
        geocentric (Earth-centered) ecliptic coordinates for the 
        requested planet are found and corrected for perturbations of the 
        other planets. Finally, the geocentric ecliptic coordinates are 
        converted to equatorial coordinates, the more familiar Right 
        Ascension and Declination. All data to this point are calculated 
        for the mean equinox of date, which appears as the Julian Epoch 
        at the right side of the window border for Display Mode 9 in the 
        form "[J1988.9]".
             The internal star database is always referenced to a 
        particular epoch; the current star database epoch is always shown 
        in Display Mode 0. The default star database epoch is J2000.0 and 
        it may be changed using Function Key F8. For consistency, 
        therefore, the planetary equatorial coordinates are also 
        automatically precessed to the current star database epoch and 
        then preset as the current target for use in Display Mode 0, the 
        Tracking Display. Therefore, having determined the current 
        coordinates for the selected planet, the user may change to the 
        Tracking Display and monitor the planet's position in equatorial 
        and horizon (observer) coordinates. Selecting a planet from the 
        Tracking Display directly by pressing "P" bypasses the Planetary 
        Data Display and shows the tracking data immediately.
             Once a planet has been selected by using "P" or Display Mode 
        9, the data is always available to the Tracking Display UNLESS 
        you select a star or other celestial object for display in the 
        meantime. If you have selected a star for display, you must again 
        select a planet with "P" before its data will be shown in the 
        Tracking Display.
             Because of the additional computational delays for the 
        "average" micro-computer when processing a planet's equatorial 
        coordinates in the Tracking Display, Display Mode 0, the user may 
        notice a significant "slow down" in the Tracking Display as 
        compared to the performance when a star or other fixed celestial 
        object is being tracked. The additional calculations related to 
        planetary position are only performed when a planet is selected 
        for display.
             Two display screens are available for the selected planet in 
        Display Mode 9: Planetary Data (default) and Orbital Data. 
        Pressing the PgUp, PgDn, or "9" keys will switch between the two 
        displays. The sample displays shown below were taken for MARS at 
        00:00 UT on 8 November 1988 and ASTROCLK's star epoch was 
        J2000.0. As with other ASTROCLK data, the reader is reminded that 
        the accuracy of the data is not necessarily as good as the 
        precision displayed; this is particularly true of the planetary 
        data, given the complexity of the calculations. See the section 
        PRECISION AND ACCURACY TESTS for additional discussion.
             Because of the differences among printers, the degree symbol 
        (which appears on the displays) has been deleted from all sample 
   ASTROCLK Astronomical Clock and Celestial Tracking Program        Page 62


        displays, and the symbols omega and theta zero have been deleted 
        for the Longitude of the Ascending Node and the Angular Diameter 
        at 1 AU, respectively, in the Orbital Display.

        MARS Planetary Data                           [J1988.9]
        -------------------------------------------------------

             Heliocentric Longitude:          29 59'44.09"
             Heliocentric Latitude:           -0 37'00.40"
             Heliocentric Radius (AU):         1.4320914  
             Appar Geocentric Longitude:       0 34'28.42"
             Appar Geocentric Latitude:       -1 36'23.79"
             Geocentric Distance (AU):         0.5498746  
             Apparent Right Ascen [J1988.8]:   0:04:41.06 
             Apparent Declination [J1988.8]:  -1 14'36.50"
             Apparent Right Ascen [J2000.0]:   0:05:15.32 
             Apparent Declination [J2000.0]:  -1 10'53.20"
             Ang Size (") & Vis'l Mag:     17.02    -1.97   

             The Heliocentric Ecliptic Longitude, Heliocentric Ecliptic 
        Latitude, Heliocentric Radius, and Geocentric Distance are the 
        instantaneous values corrected for perturbations but not for 
        light time; they are therefore the true values for the given 
        instant. The Geocentric Ecliptic Longitude and Geocentric 
        Ecliptic Latitude have been corrected for perturbations, light 
        time, nutation, and aberration and are therefore the apparent 
        values for the given instant.
             The two sets of equatorial coordinates, apparent right 
        ascension and apparent declination, are calculated for two 
        different epochs. The first set is calculated for the current 
        time and date and is therefore for the Mean Equinox of Date 
        (J1988.9 in the samples, also shown at the upper right of the 
        window border). The values for the second set of equatorial 
        coordinates have been precessed to the current epoch for 
        ASTROCLK's internal star database; the default epoch for the 
        internal star database is J2000.0, as shown in the sample above. 
        Precessing the internal star database using Function Key F8 will 
        change the epoch used for these coordinates. It is this last set 
        of coordinates, referenced to the current star database epoch, 
        which is automatically transferred to Display Mode 0, the 
        Tracking Display, where the same data is displayed, and is 
        converted to horizon coordinates and corrected for refraction. 
        The apparent size in arcseconds and the approximate visual 
        magnitude are shown on the last line of the display.
             Care must be taken when comparing ASTROCLK's planetary data 
        with other sources to ensure that the data are calculated for the 
        same time, date, and epoch. For example: the Astronomical Almanac 
        and the USNO Floppy Almanac use Terrestrial Dynamical Time (TDT) 
        and provide positions as of the Mean Equinox of Date; Bretagnon 
        and Simon use UT (internally converted to TDT/ET) and calculate 
        positions as of the Mean Equinox of Date but use the Zero Year 
        date numbering system for years "BC"; Sky & Telescope Magazine 
        provides sample planetary data each month which is calculated 
        using Universal Time (0 hours UT) and the Mean Equinox of Date; 
        and, Astronomy Magazine does not specify a time scale or time for 
   ASTROCLK Astronomical Clock and Celestial Tracking Program        Page 63


        its monthly planetary calculations but data is marked Epoch 
        J2000.0.

        MARS Orbital Data                             [J1988.9]
        -------------------------------------------------------

             L Mean Longitude:                21 40'41.18"
             _ Mean Daily Motion in Long:      0 31'26.65"
             w Longitude of Perihelion:      335 51'13.93"
             e Eccentricity:                   0.09339464 
             i Inclination:                    1 50'59.08"
               Longitude of Asc Node:         49 28'17.35"
             a Semi-Major Axis (AU):           1.52368830 
               Ang Diameter @ 1 AU (arcsecs)   9.36
               Std Visual Magnitude [V(1.0)]  -1.52

             The Mean Longitude, Longitude of Perihelion, Eccentricity, 
        Inclination, Longitude of the Ascending Node, and the Semi-Major 
        Axis are the six standard orbital elements used for calculating 
        the instantaneous position of a planet in its orbit about the 
        Sun. [NOTE: Some authors use the Argument of the Perihelion 
        instead of the Longitude of the Perihelion.] The Mean Daily 
        Motion in Longitude is derived from the Mean Longitude as a 
        function of time. The Angular Diameter at 1 AU is the standard 
        angular diameter measured at a distance of 1 Astronomical Unit. 
        Similarly, the Standard Visual Magnitude shown is the standard 
        visual magnitude measured at a distance of 1 Astronomical Unit.
             The calculation of the positional data for a selected
        planet requires first that the orbital elements for all planets 
        be calculated. The orbital elements are then used to compute the 
        perturbations affecting the selected planet. Only the orbital 
        elements for the selected planet are shown in the Orbital Data 
        Display and only the last three items in the display are 
        constants. All other data must be re-computed for each instant.
             After a planet has been selected, switching to the Tracking 
        Display, Display Mode 0, will show the usual tracking data for 
        the selected planet updated once per second or as rapidly as the 
        micro-processor can manage (degree symbol deleted):

        P4   MARS (Automatic)
        ---------------------

             EQUATORIAL COORDINATES [J2000.0]:             
               RIGHT ASCENSION (hours):         0:05:15.32 
               DECLINATION (degrees):          -1 10'53.20"
               HOUR ANGLE (hours):             19:10:42.68 
             APPARENT COORDINATES [J1988.8]:               
               RIGHT ASCENSION (hours):         0:04:41.06 
               DECLINATION (degrees):          -1 14'36.52"
               HOUR ANGLE (hours):             19:11:16.94 
             OBSERVER HORIZON COORDINATES:                 
               ALTITUDE [Hc] (degrees):        14 01'20.61"
               AZIMUTH  [Zn] (degrees):       101 10'41.66"
               Apparent ALTITUDE (degrees):    14 04'59.95"
             [Charts SA=17 U=I/II-215]       [VMag = -1.97]
   ASTROCLK Astronomical Clock and Celestial Tracking Program        Page 64


        
        MINOR PLANET SELECTION

             The current complete Minor Planet Catalog as of this 
        writing, ELEM1989.001 for March 15, 1989 compiled by E. G. Bowell 
        of the Lowell Observatory, lists 3,774 minor planets and their 
        various orbital parameters. This is far too much data for direct 
        inclusion in ASTROCLK; in conventional ASCII format, the full 
        Minor Planet Catalog requires over 380K bytes of disk storage. In 
        addition, reading the ASCII data and converting the parameters to 
        the internal numerical formats required by ASTROCLK requires 
        extra computational time. I have therefore designed a compressed 
        Minor Planet Catalog format for use with ASTROCLK; the 
        compression to ASTROCLK's MPC format, along with data examination 
        and recreation of the original ASCII format, if desired, is 
        performed by program MPCAT. The resulting MPC format file, 
        ELEM891.MPC, requires approximately 241K bytes for the full 
        catalog, still quite a bit if you don't happen to be interested 
        in minor planets. Therefore, an abbreviated version of the full 
        catalog, ASTROCLK.MPC, containing the first 250 minor planets is 
        included with the standard distribution of ASTROCLK and only 
        requires approximately 64K bytes. The full MPC catalog is 
        available from my bulletin board system. (See A BRIEF EDITORIAL 
        for further information.)
             Unlike the major planets, no "general theory" exists for the 
        complex motion of the many minor planets; these smaller bodies 
        are not only subject to the influence of the major planets but 
        interact with each other -- and there are thousands of them in 
        the so-called "asteroid belt". There are therefore no handy time-
        dependent equations which will yield orbital and position 
        information over long time spans. Instead, so-called "osculating 
        elements", accurate for a specific date (the "epoch" of the data) 
        and referred to a specific ecliptic and equinox (the "standard 
        describe the orbit of each minor planet. Most minor planet data 
        is referenced to the standard epoch of B1950.0, although some 
        publications including the Astronomical Almanac now use J2000.0.
             When processing minor planet data, ASTROCLK first reduces 
        the raw osculating elements as read from the Minor Planet Catalog 
        in use to the equinox of date (based upon the current epoch set 
        in ASTROCLK for the internal star database), then performs all of 
        the various orbit and position calculations as of the ecliptic 
        and equinox of date. The data is then processed in the same 
        manner as for the major planets, taking into account light time 
        and yielding the apparent position for the equinox of date. The 
        data are also precessed to the current standard epoch, but 
        readers are cautioned that these data are also the APPARENT 
        position rather than the ASTROMETRIC position. In particular, the 
        Astronomical Almanac data for selected minor planets (Section G) 
        are astrometric as of Epoch J2000.0 and will therefore not agree 
        precisely with those generated by ASTROCLK.
             As the date of interest moves further from the catalog date, 
        the position calculations become progressively less accurate. 
        When possible, use a minor planet catalog which is valid for a 
        date near (within several months, for example) the date of 
        interest. ASTROCLK displays the osculation date for the external 
   ASTROCLK Astronomical Clock and Celestial Tracking Program        Page 65


        catalog in the form DD-MM-YYYY, but no check is made for 
        excessive time spans. See also the section PRECISION AND ACCURACY 
        TESTS for further discussion.
             Before attempting to use the Minor Planet Catalog, use 
        Function Key ALT-F10 to verify that the path and file name for 
        the catalog are set correctly. Particularly if you are upgrading 
        from a previous version of ASTROCLK, the file name and path will 
        probably be incorrect. As with the major planets, selection of a 
        minor planet begins by pressing the letter "P" for Planet 
        Selection, then press "X" to select the Minor Planet Catalog. 
        Information about the catalog is then displayed and the minor 
        planet number is requested:

                  MINOR PLANET SELECTION

                  Minor Planet SOURCE file:   ELEM1989.001
                    [SOURCE: E G BOWELL, LOWELL OBSERVATORY]
                  Minor Planet CATALOG file:  ASTROCLK.MPC
                  Minor Planet Data Date:     15-03-1989
                  Minor Planet Ecliptic Date: B1950.0
                  First Minor Planet:         1
                  Last Minor Planet:          250
                  Total Minor Planets:        250

                  Enter Minor Planet NUMBER:
                  [Press RETURN to enter NAME]

        Enter the desired minor planet number, followed by RETURN, or 
        press RETURN alone and receive the prompt to enter the minor 
        planet name:

                  Enter Minor Planet NAME:
                  [Press RETURN to cancel]

        Enter the desired minor planet name, followed by RETURN, or press 
        RETURN again to cancel the name request and return to the main 
        Minor Planet Selection menu. When entering a minor planet name, 
        upper or lower case may be used and only sufficient letters are 
        required to unambiguously identify the desired minor planet. For 
        example, to search for VICTORIA you might enter simply "VIC" or 
        "vic". ASTROCLK will search the catalog for any minor planets 
        whose name begins with the letters VIC.
             When possible, use the minor planet NUMBER rather than the 
        minor planet NAME. ASTROCLK can retrieve the data directly when 
        the number is given, but must search through the entire file 
        looking for a match to the name. Depending upon the type and 
        speed of your disk system, the time difference can be very 
        considerable!
             Once ASTROCLK has located the requested minor planet or one 
        which matches the requested name, the data for that minor planet 
        is displayed:

                  Minor Planet 12:             VICTORIA
                     Ecliptic Epoch:           B1950.0
                     Orbital Elements Date:    15-03-1989
   ASTROCLK Astronomical Clock and Celestial Tracking Program        Page 66


                  M  Mean Anomaly:             334.29342
                  w  Argument of Perihelion:    68.76240
                     Long of Ascending Node:   235.12759
                  i  Inclination:                8.37950
                  e  Eccentricity:               0.21976110
                  a  Semi-Major Axis:            2.33431886 AU
                  B  Std Blue Magnitude @ 1AU:   7.23

        If a minor planet number was requested, the following prompt will 
        also appear:

                  Press RETURN to ACCEPT, SPACE to cancel:    

        As indicated, press RETURN to accept the minor planet or press 
        SPACE to return to the main Minor Planet Selection menu. If a 
        minor planet name was requested, the following prompt will appear 
        instead:

                  Press RETURN to ACCEPT, SPACE to continue:

        If this is the desired minor planet, press RETURN to accept it. 
        If you wish ASTROCLK to search further for another match to the 
        requested name, press SPACE. The process will continue until a
        minor planet is accepted or until the end of the catalog has been 
        reached.
             Once accepted, the minor planet data is treated in almost 
        the same manner as that for a major planet. The positional data 
        will be automatically displayed, unless Display Mode 0 was 
        selected (degree symbol omitted):

                  VICTORIA Positional Data            [J1989.1]
                    [Osculating elements as of 1989 MAR 15]
                  Heliocentric Longitude:         252 37'40.34"
                  Heliocentric Latitude:            2 32'11.13"
                  Heliocentric Radius (AU):         1.9520963
                  Appar Geocentric Longitude:     275 40'38.95"
                  Appar Geocentric Latitude:        2 02'35.38"
                  Geocentric Distance (AU):         2.4224614
                  Apparent Right Ascen [J1989.1]:  18:24:21.39 
                  Apparent Declination [J1989.1]: -21 16'48.43"
                  Apparent Right Ascen [J2000.0]:  18:25:00.46 
                  Apparent Declination [J2000.0]: -21 16'25.01"
                  Blue Photographic Magnitude [B]: 10.65

        Pressing "9" will display the orbital data. (NOTE: The pi and 
        omega symbols associated with Longitude of the Perihelion and 
        Longitude of the Ascending Node, as well as the degree symbol, 
        have been omitted from this text but appear on the display.)

                  VICTORIA Orbital Data               [J1989.1]
                    [Osculating elements as of 1989 MAR 15]
                  M Mean Anomaly:                 326 33'52.52"
                  L Mean Longitude:               271 00'02.48"
                  n Mean Daily Motion in Long:      0 16'34.86"
                    Longitude of Perihelion:      304 26'09.94"
   ASTROCLK Astronomical Clock and Celestial Tracking Program        Page 67


                  w Argument of Perihelion:        68 43'54.29"
                  e Eccentricity:                   0.21976110 
                  i Inclination:                    8 22'37.22"
                    Longitude of Ascending Node:  235 42'15.65"
                  a Semi-Major Axis (AU):           2.33431886 
                  q Perihelion Distance (AU):       1.82132638 
                  T Perihelion Date:        1985 NOV 21.338043 
                                                  [B =  7.23]

        Pressing "0" will select the Tracking Display, as usual, and the 
        data for the minor planet will have been automatically 
        transferred as with the major planets. The tracking data display 
        corresponding to the minor planet VICTORIA indicates the usual 
        data with the prefix "MP #nn", where "nn" is the Minor Planet 
        Number as read from the Minor Planet Catalog. A parenthetical 
        reminder that the data originated with the Minor Planet Catalog 
        is included. The following sample illustrates the data presented:

                  MP #12 - VICTORIA (MP Catalog)

                  EQUATORIAL COORDINATES [J2000.0]:
                    RIGHT ASCENSION (hours):        18:25:00.46 
                    DECLINATION (degrees):         -21 16'24.98"
                    HOUR ANGLE (hours):              7:55:04.82 
                  APPARENT COORDINATES [J1989.1]:
                    RIGHT ASCENSION (hours):        18:24:21.39 
                    DECLINATION (degrees):         -21 16'48.43"
                    HOUR ANGLE (hours):              7:55:43.90 
                  OBSERVER HORIZON COORDINATES:
                    ALTITUDE [Hc] (degrees):       -35 21'31.90"
                    AZIMUTH  [Zn] (degrees):       269 30'45.70"
                    Apparent ALTITUDE (degrees):   -35 21'31.90"
                  [Charts SA=22 U=II-339]         [BMag = 10.65]


        Entering Orbital Parameters

             You may also enter the orbital parameters for an orbiting 
        body directly. The orbital parameters are the same as those used 
        for the minor planets. In this case, use the "Z" selection on the 
        planet selection menu. The following data are required:

                     Object Name
                     Ecliptic Epoch
                     Elements Date (D,M,Y)
                  M  Mean Anomaly
                  w  Argument of Perihelion
                     Long of Ascending Node
                  i  Inclination
                  e  Eccentricity
                  a  Semi-Major Axis
                  B  Std Blue Mag @ 1AU

             In order to determine an elliptical orbit, six orbital 
        parameters are required, often referred to as "osculating 
   ASTROCLK Astronomical Clock and Celestial Tracking Program        Page 68


        elements". To these are added the ecliptic date of the data (to 
        determine the coordinate system used) and the date of the 
        parameters. Since this function is patterned after the minor 
        planet function, the standard blue photographic magnitude 
        measured at one Astronomical Unit is also requested.
             Each item shown in the list above will be requested in turn. 
        The Object Name may be entered in upper or lower case letters but 
        will be converted to all upper case letters by ASTROCLK. For most 
        minor planets and similar bodies, the Ecliptic Epoch is B1950; 
        enter the epoch as either Besselian or Julian, designated by the 
        letter prefix "B" or "J" (upper or lower case) respectively, 
        followed by the full epoch year and optional decimal fraction 
        (e.g. B1950.0). The Elements Date is the date for which the 
        orbital parameters are accurate; enter as day-month-year or by 
        any of the other date formats used with Function Key F3; 
        regardless of the input format used (calendar date, julian date, 
        epoch, etc.), ASTROCLK will convert the information to standard 
        calendar date. The position of an orbiting body may generally be 
        calculated for dates within a few months of the date of the 
        orbital parameters and still retain reasonable accuracy.
             Once all of the orbital parameters and other data have been 
        entered, they will be displayed again, as interpreted by 
        ASTROCLK, along with the following message:

                  Press RETURN to ACCEPT, SPACE to cancel:    

        If the data are correct, press RETURN; if not, press the SPACE 
        BAR and the data will be discarded. Operation from this point is 
        identical with normal minor planet selection above.
