The Moon has been worshipped by primitive peoples and has inspired humans to
create everything from lunar calendars to love sonnets, but what do we really know about
it? The most accepted theory about the origin of the Moon is that it was formed of the
debris from a massive collision with the young Earth about 4.6 billion years ago. A huge
(5)body, perhaps the size of Mars, struck the Earth, throwing out an immense amount of
debris that coalesced and cooled in orbit around the Earth.
The development of Earth is inextricably linked to the moon; the Moon’s
gravitational influence upon the Earth is the primary cause of ocean tides. In fact, the
Moon has more than twice the effect upon the tides than does the Sun. The Moon makes
(10)one rotation and completes a revolution around the Earth every 27 days, 7 hours, and 43
minutes. This synchronous rotation is caused by an uneven distribution of mass in the
Moon (essentially, it is heavier on one side than the other) and has allowed the Earth’s
gravity to keep one side of the Moon permanently facing Earth. It is an average distance
from Earth of 384,403 km.
(15)The Moon has no atmosphere; without an atmosphere, the Moon has nothing to
protect it from meteorite impacts, and thus the surface of the Moon is covered with impact
craters, both large and small. The Moon also has no active tectonic or volcanic activity, so
the erosive effects of atmospheric weathering, tectonic shifts, and volcanic upheavals that
tend to erase and reform the Earth’s surface features are not at work on the Moon. In fact,
(20)even tiny surface features such as the footprint left by an astronaut in the lunar soil are
likely to last for millions of years, unless obliterated by a chance meteorite strike. The
surface gravity of the Moon is about one-sixth that of the Earth’s. Therefore, a man
weighing 82 kilograms on Earth would only weigh 14 kilograms on the Moon.
The geographical features of the Earth most like that of the Moon are, in fact, places such
(25)as the Hawaiian volcanic craters and the huge meteor crater in Arizona. The climate of the
Moon is very unlike either Hawaii or Arizona, however; in fact the temperature on the
Moon ranges between 123 degrees C. to –233 degrees C.