
                                      ASTRO
                               An Astronomy Program
                                  By Don Thayer
                                  January 3,1987
      
                                Files description:
             ASTRO.COM  ...... Standard EGA Astronomy Program
             ASTRO87.COM ..... EGA with 8087 Coprocessor Version
             ASTRO.TXT ....... This Document
      
      Please note:  Both these programs require an EGA card to run.
         ASTRO87.COM also requires a 8087 math coprocessor.  Both programs
         check for the presence of an EGA card, however, ASTRO87.COM will
         hang a computer that does not have the  8087.
      
      The algorithms for calculating data for "Orbital Data of Planets" and
      "Rise and Set Times" were translated to Turbo Pascal from a basic
      language book titled "Celestial Basic" by Eric Burgess published by
      Sybex.
      
      From the Selection Menu, you can choose four different astronomy
      routines.  Whenever you quit from one of these routines, you will be
      returned to this menu.  To exit from the program altogether, press the
      "Q" key from the Selection Menu.
      
                         ****** ASTRONOMY ROUTINES ******
      
      ORBITAL DATA OF PLANETS:
      This routine calculates the Heliocentric Longitude (in degrees),
      Distance from the Sun (in AU), Right Ascension (in hours), Declination
      (in degrees) and the Distance From the Earth (in AU).  Once the data
      has been displayed, the following line will be displayed at the bottom
      of the screen:
      
            G = Graph    P = Print    N = New Date    Q = Quit
      
      Press the "G" key for a graphic representation of the solar system.
      Press the "P" key for the data to be printed on the printer.  Pressing
      the "N" key will prompt you for a new date and pressing the "Q" key
      will return you to the Selection Menu.
      
      If you choose to print the data on a printer, the program will ask if
      you want to advance the printer.  Pressing the "Y" key will advance
      the printer to the top of the next sheet. This option was added
      because you can print up to any two sets of data on one sheet if you
      wish.
      
      The graphics of the solar system shows relation ship between the
      planets and although the distances between the orbits are
      proportional, the orbits themselves are circular instead of the true
      elliptical ones.
      
      The orbit of pluto is not shown and for certain dates (such as Jan. 1,
      1900) the planet is off the screen.

                                     *******
      
      RISE AND SET TIMES:
      This routine will calculate the approximate rise and set times for all
      the planets plus the Sun and Moon.  Also shown is the transit time,
      R.A., declination, distance from the Earth and the angular distance
      from the Sun.
      
      After the data is displayed you may print the data on the printer,
      select a new date or quit to the Selection Menu.
      
                                     *******
      
      PHASES OF THE MOON:
      This routine requires only the Year and Month.  Once this is entered,
      the program calculates the date of the first full moon prior to the
      date entered and then will display the next three sets of dates for
      the four phases of the Moon.
      
                                     *******
      
      SOLAR SYSTEM SIMULATOR:
      This option will produce a graphic working model of the solar system.
      In addition to the year, month and day, this routine also requires the
      interval in days, the innermost planet and the Outer planet.
      
      The interval in days affects the speed at which the planets appear to
      move.  Since Mercury travels around the Sun in approximately 88 days,
      it will move fairly rapidly with a one day interval.  Pluto on the
      other hand will require an interval of several hundred days.
      
      The interval you enter must be an integer greater than zero.
      
      After the interval in days is entered, the program will prompt you for
      the "Innermost Planet Number" and then the "Outer Planet Number".
      Select the planet number from the table shown at the bottom of the
      screen.  Also the outer planet number must equal to or greater than
      the innermost planet number.
      
      If you wish, you can display all 9 planets on the screen at the same
      time, however, the inner 4 planets will only appear as a blob in the
      center of the screen.
      
      Once the simulator is running, there are several options that can be
      chosen.  These are displayed in the lower left corner or the screen.
      
      Pressing the "I" key will prompt you for a new interval.  If you wish,
      you can enter a negative number and watch the planets move backwards.
      This is helpful if you want to see a specific date again.
      
      While the simulator is running, certain information is being updated
      on the screen.  The "S" key toggles this updating on and off.  The
      writing of this data on the screen takes time and slows down the
      graphics.  Although the performance on the non-8087 version is small,
      the 8087 version can be dramatically improved by turning off the
      status.
      
      The "C" key will clear the screen and the tracing of the planets paths
      will start where the old screen left off.  This is particularly useful
      when some of the inner planets paths have made a complete revolution.
      It is also useful when you change the direction of movement using the
      "I" key.
      
      Pressing the "P" key will temporarily halt the simulator.  Press any
      other key to start it again.  If you press any of the other option
      keys, they will take effect at this time.
      
      To quit the simulator and return to the Selection Menu press the "Q"
      key.
      
                                     *******
      
      SAMPLE DEMONSTRATION:
      Start the program and select option <S> for the simulator.  Enter the
      date of May 1, 1988.  Enter an interval of one (1) and select Mercury
      as the innermost planet (1) and Mars (4) as the outer planet.  Around
      June 13,1988 you should see the opposition of Mercury, Venus and
      Earth.  A little later in the same year, around September 26 you
      should see the opposition of Earth and Mars.  You may want to compare
      the the Heliocentric Longitude's of these planets for these dates
      using option <O> from the Selection Menu.
      
                                     *******
      
      ACCURACY:
      This program is by no means exact.  To the best of my knowledge it is
      fairly accurate, however, there are a number of astronomical
      corrections not allowed for such as precession.  Also much of the
      original data was limited to only a few significant figures.
      Admittedly this makes poor use of the 8087 with its 16 digit accuracy.
      
      From an astronomer's point of view, my knowledge of astronomy is nil
      and of the related math, it is even less.  There are several very good
      astronomy program available for the PC, however, none of them that I
      have found combine the planetary data and graphics the way this one
      does.
      
      If you have any comments, suggestions or information on how I can
      increase the accuracy of this program, please write to me at the
      following address:
      
                        Don Thayer
                        1675 Hays St. #207
                        San Leandro, Ca  94577
      
      The programs ASTRO.COM and ASTRO87.COM along with this document file
      may be distributed freely among users and user groups in their
      original and unmodified form.  No profit either monetary or otherwise
      shall be gained from the sale of these programs.


