File GALILEO.ZIP from The Programmer’s Corner in
Category Science and Education
Plots the motion of the four largest of Jupiter’s moons — the Galilean Satellites.
File Name File Size Zip Size Zip Type
GALILEO.DOC 2514 1270 deflated
GALILEO.EXE 45587 29945 deflated

## Contents of the GALILEO.DOC file

DOCUMENTATION: GALILEO.EXE version 1.2

When Galileo turned his newly-made telescope to the sky in the 15th
century, he discovered that the planet Jupiter had four "stars" that
circled around it. These were the moons Io, Europa, Ganymede, and
Callisto, now called the Galilean Satellites in his honor.

GALILEO.EXE is a program that calculates and plots the motion of these
moons on your monitor. GALILEO.EXE is written in Turbo Basic and senses
the video hardware and configures itself accordingly for VGA, EGA, and
CGA. I have not written a Hercules driver, nor does it work with an EGA
card driving a CGA monitor, though it does work with EGA monochrome.
GALILEO will also use a math coprocessor if present.

You will be prompted for the orientation of the display, either
East or West to the left, matching the display of binoculars or
astronomical telescopes, respectively. Reply E or W to the
prompt, or Q to Quit.

The motion is displayed as a 12-day scroll, with ticks plotted at
00:00 Universal Time (Greenich Mean Time) for each passing day,
allowing one to see the motion over time and estimate the time of
interesting groupings.

The program works like this:

1. Calculate where each moon is in its orbit around Jupiter.
2. Calculate where Jupiter is in its orbit.
3. Calculate where the Earth is in its orbit.
4. Solve the geometry problem for the way that we see the
moons from the Earth.

The results gives very acceptable accuracy for most purposes.
There are several factors that I have not included in the
calculations that would improve the precision to enable the
prediction of eclipses and transits, namely the inclination of
our mutual orbits and the correction for the transit time of light
from Jupiter. I may get around to this eventually, but for now,
the program suits my requirements.

I hope that you will feel motivated to see these moons for yourself.
Any small modern telescope will be superior to even the best instrument
that Galileo ever had. Binoculars will also show all four moons, if
they are mounted steadily. A small telescope at about 50 times gives a
very nice view.

Can't find Jupiter?? Consult Astronomy Magazine, Sky and Telescope,
watch the Star Hustler on PBS, or give me a call at 703-773-2564 during
the evenings. In any case, get out and observe!

Donnie S. Coleman
Rt. 2 Box 724
Independence, Virginia 24348
6 April 1991

December 12, 2017