The Moon a base for many Aliens
The Moon is a piece of rock next to Earth. Under Galatic Law the Moon is considered Neutral. It has been seen as a base for the Cybermen. The Cybermen tried to attack Earth as there homeworld of Mondas was destroyed. They fought with Earth for centuaries until UNIT had defeated them.
The Ice Warriors also used the Moon to send their pods to Earth so that they could invade Earth in 2170. By this time the moon was used to contol the Earth's weather.
In 2540 the Moon was used as a prison where if you did something terrible on Earth you were to be sent to the prison forever.
At one point the New Hope Hospital was transported there by the Judoon to catch an alien criminal a Plasmavore. The Judoon landed on the Moon and stomped right across it to to hospital. In the end the Judoon killed the Plasmavore and left the Moon.
The Cybermen had many other attempts like when they tried to make Halley's Comet crash into Earth again this was for revenge. There plan yet again failed. They tried another time as they waited on the Dark Side of the Moon. They wanted to control the Nemesis Statue so that they could destroy Earth. The Doctor foiled their plans and destroyed them.
In the Sarah Jane Adventures the Slitheen wanted revenge on Sarah Jane mostly a Slitheen called Carl. Them and the help of Mr Smith tried to make the moon crash into Earth. The Slitheen realised they had been tricked so Sarah Jane destroyed Mr Smith.
The Moon has appeared in:
Season 4: The Moonbase
Season 6: The Invasion and The Seeds of Death
Season 10: Frontier in Space
Season 22: Attack of the Cybermen
Season 25: Silver Nemesis
Series 2: Tooth and Claw
Series 3: Smith and Jones
Series 1 of Sarah Jane Adventures: The Lost Boy
Series 4 of Sarah Jane Adventures: Death to the Doctor