Stormin Mormon wrote:
It's been a long time since grade school. But I some how
remember that one side of the moon is always light, the
other always dark.
Nope.
If keeps one face toward us (more or less).
We never see the other side of the moon.
But the Sun does - about 1/2 of the time.
From Wiki
http://en.wikipedia.org/wiki/Orbit_of_the_Moon
Libration
Animation of the Moon as it cycles through its phases. The apparent wobbling of
the Moon is known as libration.
The Moon is in synchronous rotation, meaning that it keeps the same face turned
toward the Earth at all times. This synchronous rotation is only true on average
because the Moon's orbit has a definite eccentricity. As a result, the angular
velocity of the Moon varies as it moves around the Earth, and is hence not
always equal to the Moon's rotational velocity. When the Moon is at its perigee,
its rotation is slower than its orbital motion, and this allows us to see up to
eight degrees of longitude of its eastern (right) far side. Conversely, when the
Moon reaches its apogee, its rotation is faster than its orbital motion and this
reveals eight degrees of longitude of its western (left) far side. This is
referred to as longitudinal libration.
Because the lunar orbit is also inclined to the Earth's ecliptic plane by 5.1°,
the rotation axis of the Moon seems to rotate towards and away from us during
one complete orbit. This is referred to as latitudinal libration, which allows
one to see almost 7° of latitude beyond the pole on the far side. Finally,
because the Moon is only about 60 Earth radii away from the Earth's center of
mass, an observer at the equator who observes the Moon throughout the night
moves laterally by one Earth diameter. This gives rise to a diurnal libration,
which allows one to view an additional one degree's worth of lunar longitude.
For the same reason, observers at both geographical poles of the Earth would be
able to see one additional degree's worth of libration in latitude.
--
Richard Lamb
http://www.home.earthlink.net/~cavelamb/