Name: Kepler
               Version: 1.0
                  Date: 26 April 1991
            Authors(s): James E. Hetrick
               Contact: J.E. Hetrick (hetrick@phys.uva.nl)
       Subject Area(s): Astronomy, Education
   News Group or Email: hetrick@phys.uva.nl
        Bug reports to: hetrick@phys.uva.nl (Jim Hetrick)
       Software Needed: egavga.bgi 
       Hardware Needed: IBM PC, VGA graphics card
             User Base: Watchers of the sky
         Documentation: KEPLER.TXT (Sorry). 
  Published References: The algorithms were taken from Duffet-Smith's
                        book, "Practical Astronomy with your Calculator".

              Abstract: 

Kepler was originally meant to be just a toy for myself, to be
used to compute the angles of the planets along the ecliptic, to
facilitate watching the planets move throughout the year.

Upon startup, one is prompted for the date, to which one can enter "0"
for today. Next one must enter the number of planets in the view,
followed by [Y/N] for including comet Halley. It then displays the
Solar System from "above" (perp. to the Earth's orbit). ESC (the
Escape key) exits Kepler.

Kepler provides and "[O]verlay" which draws lines to the planets, and
computes the angle along the ecliptic from the Sun rise/set. The
overlay also has a cross centered on the Earth which can be rotated to
show the Earth's rotation. The cross is rotated by [t] (rotate Earth
forward one 1/2 hour) and [T] (ie. Shift-t, rotate Earth backward).

Additional features include comet Halley and its orbit, and two views
of the [M]oon: one window of the Earth-Moon system (from "above"), and
the Moon as seen from Earth, ie. it's phase.

All the above features move under the [A]nimation key, which increments
the date and redisplays the planetarium. The speed of this depends on
your machine, but is quite reasonable on even a 16Mhz box.

This code is under development. I envision a much more interactive,
mouse based educational astronomy package, which would include
clicking on planets to brings up Voyager gifs, data files, etc.  It
needs to be ported to C++, X, and other platforms. If you're
interested in helping, please contact me.

Synopsis of commands:

	[a]:  Toggle animation of planitarium on/off
	[r]:  Reset to original date

	[b]/[f]: Backward/Forward on day

	[o]: Overlay
	     [t]/[T]: Rotate Earth 1/2 and hour forward/backward

	[m]: Toggle display of the Moon

	[ESC]: Exit Kepler


Jim Hetrick
hetrick@phys.uva.nl