Why is the moon grey?

Is it grey?

The moon looks grey, but astronauts who walked on the moon saw lots of different colours, like black, brown, olive green and white. Some of the rocks even have glass in them.

When we see the moon from the earth, those colours look grey.

The moon looks mainly light grey, but there are some dark grey patches. These patches can sometimes make shapes that we recognise, like The Rabbit on the Moon and The man in the Moon.

The astronauts say they didn't see any real rabbits hopping around on the moon.

What is the light grey rock?

When the earth was very new another planet smashed into it and a piece broke away. That piece was so hot that it became molten (that means the rock became a liquid) and gravity made it form into a ball. When it cooled down it turned back into rock and was called The Moon.

So the light grey rock is simply the earth's crust. That rock is called anorthosite breccia, but moon experts often just say breccia.

Breccia rock

What is the dark grey rock?

When lava erupts it flows in long rivers and comes to rest in big lava lakes. When the lava cools down, it turns into rock. That rock is very dark. It is called basalt.

While the moon was still hot, a lot of lava erupted through its crust when asteroids and meteors hit it.

The dark grey patches on the moon are seas of lava that have turned to basalt rock.

Apollo 11 landed on an old lava sea, called The Sea of Tranquility. The astonauts picked up lots of rocks from there.

Basalt rock

How do we know this?

For a long time, people didn't know what the moon was made out of. So we sent astonauts to the moon to pick up some rocks and bring them back to earth.

12 astonauts have walked on the moon in expeditions called The Apollo Missions.

A really clever scientist would make a bar chart of the rock types. If the bar chart had one big bar of breccia and another bar, about half as big, of basalt, then the scientist could say she was sure the rocks came from the earth.

Many scientists put their bar charts in a report or in a PowerPoint presentation.

A scientist's bar chart, proving the moon came from the earth.

But if the moon comes from the earth, why isn't it blue and green, like the earth?

There is no water on the moon. Life cannot exist without water.

On the earth, the blue colour that we see is the water reflecting the sky, and the green colour is life (such as plants and trees).

The moon is grey because there is no water and, therefore, no life on it.

A photo of the earth taken from Apollo 8.