The Moon is a heavenly body. Any heavenly body that revolves round a planet is called its satellite. The Moon revolves round the Earth. Therefore, it is called a satellite of the Earth.
The Moon is the only satellite on which man has landed. On July 20, 1969, Neil Armstrong, an American astronaut, succeeded for the first time in landing on the Moon’s surface in Apollo 11 flight and unravelled many mysteries about it. In this very flight, a retro-reflector was mounted on the Moon’s surface. Laser beams sent from the Earth’s surface and reflected back by this retro-reflector enabled scientists to calculate the exact distance of the Moon from the Earth. The distance so calculated has an accuracy of less than 15 cm. The distance has been calculated to be 3, 84,400 km.
The Moon is a solid spherical body like a football. It completes one revolution round the Earth in an elliptical path in a period of 29 days 12 hours and 43 minutes. We call this period a lunar month. Only one side of the Moon is always visible to us because the period of its rotation on its axis is approximately the same as the period of its revolution round the Earth.
The Moon does not have its own light but shines due to the Sun-light. Ten percent of the Sun’s light falling on the Moon is reflected by its surface while the rest is absorbed by it. During noon, the surface temperature of the Moon is about 130°C, while, during the night, it is very cold. The Moon’s surface is very uneven. There are mountains, valleys and black plains on the Moon’s surface. These black portions appear as lunar spots. There are heaps of ashes on its surface caused by the fall of meteors. The diameter of the largest crater on the Moon is 232 km which is 365.7 metres deep. Studies on the samples of rocks collected from the Moon’s surface have revealed that they contain metals like aluminium, iron, magnesium etc. The lunar surface contains silicates also. The Moon does not have air and water and, therefore, there are no signs of life there.
The average distance of the Moon from the Earth keeps on changing slightly because of the Moon’s elliptical orbit. The diameter of the Moon is approximately 3476 km. It rotates on its axis with a speed of 3430 km per hour. The Earth is about 81.3 times heavier than the Moon and 49 times larger in volume. The force of gravity on the Moon is one-sixth that of the Earth. Scientists are making constant efforts to obtain more and more information about the Moon.
