The Moon's orbit, we can talk about is apogee and it's perigee.

Apogee is the maximum distance the Moon is from the Earth.

It's about 405,000 kilometers.

And perigee's a bit smaller, 363,000 kilometers.

These two are pretty close.

So, the Moon's orbit is close to circular.

As I've mentioned already, the Moon's fairly large.

Its radius is about 1,700 kilometers,

or about a quarter of the radius of the Earth.

And it's mass is about 1% of the earth's mass.

Taking that mass and radius we can work out it's density and

the density of the Moon is about three grams per cubic centimeter.

That compares with the earths density of about five grams per cubic centimeter.

So the composition of the Earth and Moon are different.

And as we'll discuss soon, that's a bit of a surprise, because

we would assume that the Earth and Moon were assembled from the same material.

And we would expect their composition to be similar.

If we look at the structure of the Moon, the Moon is mostly mantle.

It's got a thin crust.