Page 293 - NS-2 Textbook

The Moon

At one time most scientists thought that the Moon and crashing meteorites-causes extensive erosion. The con-
Earth were probably formed at the same time and in stant stream of atomic particles COIning from the Sun also
about the same way. But analYSis of hmar sample mate- causes a steady V\Tearing away of the Moon's surface rocks.
rial brought back by the Apollo missions showed sur- Among the lunar rocks returned to Earth was one
prising differences between the compositions of the that scientists labeled iglleous. This means that the rock
Moon and Earth. TI,e Moon is iron-poor, with a density was once molten, but later became solidified. This indi-
about the same as Earth's mantle. cates that the Moon, like Earth, has (or once had) a hot in-
Consequently, the favored theory now is that shortly terior and volcanoes.
after Earth cooled, it was struck a glancing blow by a Some scientists believe it possible that the Moon is
large object. The inlpact spewed material from Earth's both hot alld cold. They believe it has a cold exterior shell
mantle, which eventually came together to form the or crust, perhaps 250-625 miles deep, surrOlUlding a
Moon. To settle the question, more on-site reseal'eh needs warm belt of rock, and possibly even a molten core. This
to be done, perhaps using a base camp that might one would make it much like Earth-except that Earth's
day be established on the hmar surface. outer ClUSt, called the lithosphere, is only about 15 miles
The Moon's diameter is 2,160 nilles, roughly 30 per- thick.
cent that of Earth. The Moon is generally said to be The surface walked on by the Apollo astronauts was
about 239,000 miles away frOlll Earth; this, however, is covered by breccia. There also is a layer of dust made up
an average distance. TIle distance actually varies from of tiny glass tektites. These little spheres are no bigger
about 226,000 nilles at the closest to 252,000 miles at the than sand granules, and sonle are microscopic in size.
farthest. TIley are multicolored, with hues ranging from dark
The Moon circles Earth every 27)0 days. It also com- brown to yellow to clear. Tektites make lip one-quarter to
pletes one rotation about its axis in the same time period,
which accounts for the fact that the Moon always has the
same side facing Earth. In other words, the Moon rotates
once on its axis and revolves once arolmd Earth in the
same length of time.
The Moon has no atmosphere. Thus, there is no grad-
ual daily temperahrre change from hot to cold, as on
Earth. On the Moon, a person partially in the slmlight
and partially in the shade would feel extreme heat and
cold at the same time. The Moon's surface temperature in
sunlight may get as high as 243 degrees F. In the dark of
the hmar night, it goes down to -261 degrees F.
Because there is no atmosphere on the Moon, there is
no sound either. Also, since there are no obscuring at-
mospheric effects, a person on the Moon can see twice as
many stars in the sky as on Earth's surface.

MOON GEOLOGY
Erosion on the Moon takes place very slowly because
there is no rain or ,vind. Ho'vevel~ our astronauts A test director at the Lunar Receiving Lab looks at basketball-sized
learned that the spray of the breccia-broken rocks from Moon rocks through a microscope.

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