Notes The Moon

The Moon is about 240,000 miles away from Earth. This is about 100 times the distance between New York and Los Angeles.

The Apollo spacecraft took about 3 days to reach the Moon.

The Moon Rotates You may have noticed that the full Moon always has the same pattern of dark and light areas.

The Moon Rotates The same side of the Moon always faces Earth because it rotates at the same speed it orbits.

The Moon Rotates The half that faces Earth is called the near side. The half that faces away is called the far side.

Craters and Maria A lot of the Moon’s surface is light colored. There are also dark areas. A lot of the near side of the Moon is covered with these dark-colored features.

Craters and Maria A dark area on the Moon is called a mare Pronounced MAH-RAY Plural is maria, pronounced MAH-ree-uh Mar- sea in Latin Early astronomers thought the maria might be seas.

Craters and Maria The light colored areas of the Moon are higher than the maria, so we call them the lunar highlands.

The highlands have many impact craters. Craters and Maria The highlands have many impact craters. Many of these collisions happened long ago.

Craters and Maria Some of the large craters filled with lava that came from inside the Moon and cooled, forming the maria.

Craters and Maria Most of the large maria are on the near side of the Moon. Why?

Moon Rocks Moon rocks have different ages, just like rocks on Earth. Many rocks on the Moon are about 4.5 billion years old.

Moon Rocks Rocks in the maria are younger because they formed later, between 3.1-3.8 BYA. Most of the rock in the maria is lunar basalt.

Moon Rocks Impacts make craters, but they also break the rocks on the Moon into small pieces. This weathering has created a dry soil covering most of the Moon’s surface.

Moon Rocks Studying Moon rocks has given scientists information about the history and structure of Earth. In the Moon’s early days, it experienced impacts that made the craters we see today.

Moon Rocks The impacts on the Moon mostly ended about 3.8 billion years ago, though there have been occasional collisions since then.

Structure Just like scientists have study the surface of Earth to determine its inner structure, scientists have studied the surface of the Moon to determine the Moon’s inner structure.

Structure The Moon has three layers: a crust, a mantle, and a core.

Structure Just like on Earth, the crust is the outermost layer and is the least dense layer of rock. It is about 70 km thick.

Structure The mantle is made up of denser elements like iron and magnesium. We know this because the basalt on the surface is made of molten rock from the mantle.

Structure In the middle of the Moon is a small core, about 700 km across. Scientists think the core is made up of iron and other metals.

Formation The accepted model of the Moon’s origin is the giant impact hypothesis. In this model, Early Earth was hit by a Mars-sized planetesimal called Theia.

Formation This collision would have been about 100 million times more powerful than the asteroid impact that wiped out the dinosaurs 65 MYA.

Formation A massive ejection of rock and debris exploded into the space around Earth, which clumped together due to gravity and formed the Moon.

Formation This process may have happened in as quickly as one year!

Formation Since its formation, the Moon has moved about 3.8 cm further away from Earth every year.