Why does the Moon have dark patches?
The dark patches are huge plains of dark volcanic rock called maria, made when lava flooded giant craters billions of years ago.
If you look at the full Moon, you can see dark grey patches on its bright surface. Some people imagine they look like a face, a rabbit or a man carrying sticks.
These dark areas are called maria, which is Latin for seas. Long ago, astronomers thought they might be oceans of water. Today we know they are dry, flat plains of dark volcanic rock called basalt.
Here is how they formed. More than 3.5 billion years ago, giant space rocks smashed into the young Moon, making enormous craters called basins, some more than 1,000 kilometres wide. Later, hot melted rock from deep inside the Moon rose up through cracks and flooded these basins, like water filling a bath. When it cooled, it formed smooth, dark plains.
The bright parts of the Moon are called the highlands. They are older, covered with more craters, and made of a pale rock rich in a mineral called feldspar.
Apollo astronauts landed on several maria and brought back basalt rocks. Some meteorites found on Earth are pieces of these lunar seas, blasted off the Moon by impacts. So you might see a piece of a lunar sea in a museum!