Moon
The Moon is Earth’s only natural satellite. The diameter of
the Moon is about ¼ that of Earth, and because of the large
relation between the two, some scientists have considered The
Earth and Moon to be a double planet (3). Although the real
origin of the Moon is unknown, the most accepted theory by
scientists is that in the early stages of Earth’s formation,
an object about the size of Mars hit Earth and dug out a huge
amount of debris that came together to form the Moon (3).
Other than being relatively close in size, the Moon is quite
different than Earth. Because it has little atmosphere, it is not
protected as well from meteors and comets as Earth is. Because of
this, there is a large number of huge craters on the Moon, all of
which are still in the state as when they were formed because of
the lack of weather and erosion on the Moon (2). Unlike Earth,
the Moon does not have any volcanoes or moving crustal plates,
but there has been reports of "moonquakes" probably
caused by tides resulting from Earth’s gravitational pull
(3). The Moon is also has a different shape from the Earth in
that it looks more like an egg than a sphere (3). This
unsymmetrical distribution of mass in the Moon has caused
Earth’s gravity to constantly pull one lunar hemisphere
towards Earth. Because of this, both the Moon’s rotation
around its axis and its revolution around Earth are the same
(approx. 27 days, 7 hours, and 43 minutes) (2). Another
difference is that the Moon’s gravitational pull is about
1/6 that of Earth’s. The moon is about 384,403 km from the
Earth and its diameter is 3476 km (2).