Have you ever wondered if the Moon is made of cheese? Learn the truth about the world’s most famous satellite in this lesson packed with basic stats, orbit info, phase details, and other fun facts.
The Moon is the Earth’s largest satellite, which means that it is the largest object orbiting the Earth. It is widely believed that it formed around 4.
5 billion years ago when a large asteroid (roughly the size of Mars) crashed into the Earth. The impact likely sent a large chunk into space where the Earth’s gravity locked it into orbit.The Moon is approximately 3,475 km wide and 80 times less massive than the Earth. It appears to have a tiny iron core (680 km), a rocky mantle (1330 km), and a thin crust (70 km). The surface is pockmarked with craters of meteors which struck millions of years ago. The largest crater on the moon is the South Pole-Aitken Basin, which is nearly 2500 km (half the width of the United States) across and 8 km deep.
The Moon travels around the Earth in an elliptical orbit, with its distance from the Earth ranging from 364,397 km to 406,731 km. The orbit takes 27.3 days, which is the same amount of time that it takes the Moon to rotate on its axis. As a consequence, it has a synchronous orbit, and the same side of the Moon is always facing the Earth.
You can model this relationship with a plate and a small ball representing the Earth and the Moon respectively. Mark one side of the ball with a sticker, and place the ball at the 3:00 position with the sticker facing the plate. Now, slowly turn the ball a quarter of a turn until the sticker is pointing downward (as in the 6:00 direction); at the same time, slide the ball along the rim of the plate counterclockwise until it rests at the 12:00 position. The sticker should now be pointing down towards 6:00 (instead of to the left) and the ball is now at 12:00 (instead of 3:00). Thus, despite the revolution and rotation, the sticker side of the ball is still facing the plate. This is how a synchronous orbit causes us Earthlings to only see one side of the Moon.
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