DEMONSTRATIONS WITH THE SKYGLOBE PROGRAM



Some of the phenomena that played a prominent role in early astronomy
and the debate over geocentric versus heliocentric system can be
nicely viewed with a program called Skyglobe. To start it, go to any of
the PCs in the College computer lab in the physics and astronomy building
(room 332). Turn on the PC, and select ASTRONOMY from the menu. When
the astronomy menu comes up, select SKYGLOBE. The screen lists all
possible one-letter commands; usually capital letters go backwards,
small letters forwards. To set the viewing location, use L and try
Birmingham. The four arrow keys set the viewing direction (watch the
curved line of the horizon to keep yourself oriented).

To see Mercury and Venus move around the sun, set the time (H and T)
to noon, then go into "turbo" mode (space bar) and hit D, This advances
the sky one day at a time at noon. You will see the inner planets
move back and forth past the Sun, while the distant stars drift
across the field due to our own orbital motion.


To see retrograde motion, set the time to midnight and do as above.
Eventually you will see outer planets (Mars, Jupiter, Saturn) appear
against the (drifting) star background and execute a retrograde loop
as the Earth catches up and passes each. A good recent time is
to start tracking Mars on January 15, 1995.

Many other options are possible - for example, watching how the sky
drifts past during a single night as the Earth rotates, or seeing which
stars are circumpolar and which rise and set. Try looking at the
constellations from somewhere in the Southern Hemisphere, or better
yet compare a night's motions from both hemispheres and somewhere
on the equator. 

Watch the sun for a couple of months and notice how the Moon usually
goes well north or south of it. For a direct passage giving an eclipse,
try July 11, 1991.