The Moon

The moon is Earth's satellite. A satellite orbits or goes around a larger object. The Moon's orbit is not a perfect circle. Sometimes it is farther away from Earth than at other times. Gravity pulls the Earth and the Moon close together. Gravity is a force which pulls objects together. The Moon's gravity is one-sixth that of Earth. A person or object is pulled down to the surface of the Moon with only one-sixth the force.

The Moon is much smaller than the Earth. Its diameter is only about one quarter that of the Earth. Its diameter is 2,160 miles. A diameter is the distance from one side of a circle to the other. The distance from the Earth to the Moon is about 238, 855 miles. The average temperature on the Moon is -4 degrees Fahrenheit.

The Moon seems to change shape throughout the month. That happens because people only see the part of the Moon which the Sun lights up. The Earth travels around the Sun. The Moon travels around the Earth. When the Moon is between the Earth and the Sun, the Moon looks dark to Earth. The Sun is shining on its other side. The Moon spins on its axis once every 27 days. An axis is an imaginary line through the Moon from pole to pole.

The surface of the Moon is made up of rock and dust. The surface rock has been smashed into pieces by many meteorites. A meteorite is a rock which hits the Moon from space. Heating and cooling during the day and night also break up the rock. The surface never changes because new rock is never made as it is on Earth.

Craters on the Moon were formed by the crash of meteorites against it. The largest craters are called basins. They range in size from a few inches to hundreds of miles across. Mountains thousands of feet high stand around the rim of these basins. Rilles are deep canyons made by flowing lava. Dark areas called maria (seas) were formed when giant craters were flooded by liquid rock leaking out from under the top layer of the Moon. There is no wind or rain on the Moon to move the dust around.

In ancient times astronomers recorded the movement and shape of the Moon. They wondered why it seemed to move across the sky. The ancient Greek astronomer Hipparchus was one of the first to think that the Moon was a sphere or globe. The telescope was invented in the 1600's. People could see much more of the Moon's surface using the telescope. Scientists have sent probes to the Moon to study it. Astronauts have landed on the moon several times.

A spacecraft being launched from the Earth needs a powerful rocket to lift it. It has to overcome Earth's gravity or it could be pulled back down to Earth. The spacecraft must protect the occupants from radiation from the Sun and space. It must keep them warm and provide air to breathe. It must land safely on the Moon and protect the astronauts from the tremendous heat while re-entering Earth's atmosphere.

In summary, the Moon is a satellite which travels around the Earth. Its orbit is not a perfect circle. Sometimes the Moon is farther away from the Earth than at others. Gravity keeps the Moon and Earth together.