Heard the moon is moving away from us

[alias25]

i heard the moon is moving away from us, does that mean its orbital speed has increased? how will that affect the rotational speed of Earth on its axis? slower?

 

[Garth]

The Moon raises tides on the Earth. The Earth is rotating at a quicker rate (once per 'day') than the Moon orbits the Earth (once per 'month'). The tides in turn slow the Earth down, a phenomenon called 'tidal breaking'. As a reaction to the force raising the tides the moon 'speeds up' and slowly moves away from the Earth. I say 'speeds up' in parenthesis because as the Moon moves away from the Earth the Moon actually slows down, but it is in a higher potential energy orbit.

The Earth's rotational energy is thus transferred to the Moon's orbital energy. Eventually the Earth will always have the same 'face' turned towards the Moon, as already the Moon's nearside 'face' is always turned towards the Earth.

Garth

 

[SpaceTiger]

The Earth's rotational energy is thus transferred to the Moon's orbital energy. Eventually the Earth will always have the same 'face' turned towards the Moon, as already the Moon's nearside 'face' is always turned towards the Earth.

Though the moon's orbit is gaining energy and the Earth's rotation is losing it, it's worth pointing out that energy is not conserved between those two things. There is a significant amount of energy loss (in the form of heat and radiation) when the moon distorts the earth. There is not, however, another significant sink for the angular momentum, so it is fair to say that the angular momentum of the Earth's rotation is transferred to the moon's orbit.

 

[Plastic Photon]

I am no expert but I am quite certain that the moon orbits the Earth eliptically which means it has a perigee and an apogee.

 

[SpaceTiger]

I am no expert but I am quite certain that the moon orbits the Earth eliptically which means it has a perigee and an apogee.

This is true, but why do you bring it up?

 

[Quan Chi]

What happens if the Moon is moving too far from us? Could it lose the orbit, start wandering around and crash some other planet? Or even Earth?

 

[Garth]

What happens if the Moon is moving too far from us? Could it lose the orbit, start wandering around and crash some other planet? Or even Earth?

No - these orbital changes are tiny. However in the very far future the Moon will very slowly move back towards the Earth and - if it is still in existence then - the Moon will approach inside the Earth's Roche limit and disintegrate. The Earth may then end up moonless but with a beautiful set of Saturn-like rings!

Garth