During cloudless evenings, you can look up to the sky and see the bright Moon shining. From Earth, this object on our sky has been the source of many myths and histories. For example, animals were slaughtered on a growing moon because one thought that it would make the meat more tender, and some humans were believed to transform into werewolves with full moon. In Greek mythology, Selena was the god of the Moon, while for the Inuit’s of Greenland, the Moon god was called Anningan.
Today, we know that our moon consists of the rocks anorthosite and basalt, i.e. the light and darker patches on the its surface, and its brightness due the reflection of the light emitted from the sun. It moves around the Earth in an elliptic orbit with the average distance to Earth of 384 405 km. After the Moon solidified 4.5 billion years ago, it has been bombarded with meteorites creating all the craters at the its surface. Over the rocks, a thin layer of dust occurs, called regolith. We all remember the famous picture of the footprint left by humans on the surface on the Moon, a footprint left in regolith.
The figure illustrates one of the possible theories of how the Moon was formed, and it is to this day the leading theory of its formation. It is believed that an object collided into the Earth. The impact was so big that great amounts of dust and rocks were thrown out in the universe, where they aggregated and formed the Moon. There are other theories explaining the origin of the moon. One hypothesizes that the moon was created in proximity to Mercury and that it later wandered out in the solar system to be caught by Earth’s gravity. Another theory states that the Moon and the Earth are formed from many small particles that simultaneously gathered to form earth and moon.