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Asked by u12tsangv to Dilwar, Lou, Rachel, Simon, Susan on 16 Nov 2013.
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Susan Skelton answered on 16 Nov 2013:
Yes, the moon’s orbit is getting larger by about 4 cm ever year. It’s quite tricky to understand, but basically this is caused by the interaction of the Earth’s and moon’s gravity and the changing shape of the Earth.
As the Earth spins, the gravity of the moon causes tides on our oceans by pulling the water towards the moon. This changes the shape of the Earth very slightly, which then changes the gravitational pulling force that the Earth exerts on the moon.
Because the earth rotates much faster (24 hours) than the moon orbits the Earth (1 month), some energy is transferred from the Earth to the moon. This causes the Earth’s speed of rotation to slow down and the size of the moon’s orbit to get bigger.
This won’t cause any harm to us on Earth in the near future because the rate of slowing down is so small. However, if in the very distant future the Earth’s rotation were to slow down and stop completely, then half our planet would never see the sun! That half of the planet would be always in darkness and very very cold so the oceans would freeze and nothing would be able to survive.
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Simon Langley-Evans answered on 16 Nov 2013:
It won’t cause us any harm and the change in distance is so tiny that nobody will see any difference for many thousands of years. Maybe there will be no humans on Earth by the time the change is noticeable.
If there were people they would be missing out on one of the most wonderful sights that we get on Earth, which is a total solar eclipse. A total eclipse happens when the Earth, Moon and Sun line up perfectly so that the Moon is directly between us and the Sun. We are lucky that the moon is just the right distance away that it is exactly the size of the sun in the sky. When it is further away it will be smaller and a total eclipse will look very different.
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