The Moon is the Earth's satellite. Students are
familiar with the Moon because they see it at night. However the Moon
changes its shape from night to night. There also seems to be a cycle to
these changes. Every month the Moon goes through a cycle of phases from new
(cannot see it) to full (can fully see.) It takes 27.3 days for the Moon to
complete one orbit of the Earth. The Earth also moves relative to the Sun at
the same time the Moon is revolving around the Earth, so the Moon must
complete more than one orbit to return to the same phase as seen from
Earth. The time that the Moon takes to complete one cycle or "phases of
the Moon" is 29.5 days.
Each spot on the Moon is subjected to two weeks of day
light, during which the surface temperature reaches about 100 degrees
centigrade (boiling point). The next two weeks are night and temperatures
fall to -170 C. The Moon has no atmosphere. There is evidence that there is
water ice in some deep craters near the Moon's south pole which are
There are two primary types of terrain on the Moon:
the heavily cratered and very old highlands and the relatively smooth and
younger mare (or maria). The mare (which comprise about 16% of the Moon's
surface) are huge impact craters that were later flooded by molten lava.
Most of the surface is covered with regolith, a mixture of fine dust and
rocky debris produced by meteor impacts. For some unknown reason, the mare
are concentrated on the near side.