The sixth Doctor was intrigued by the planet Ravolox; he had found out that it had the same angle of tilt and period rotation as Earth and it is extremly rare to find two planets so similar. The similarty to Earth became more clear when the Doctor and Peri found an underground railway station - Marble Arch. The Doctor later learned that the planet Ravolox is Earth.
A group of people from Andromeda, the Three Sleepers, were stealing secrets from the Matrix on Gallifrey. The Three Sleepers were using Earth as a base for their operations. As a retribution the Time Lords dragged Earth, and it's constellation, two light years from it's usual position. A rescue ship, looking for Earth and the Three Sleepers, did not find Earth and the secrets were safe.
As a side effect nearly all life on Earth was destroyed by a fire ball. Earth later became renamed as Ravolox. The Doctor's trial was set-up by the Time Lords to hide this event, and the Doctor's adventure on Ravolox was presented as evidence.
Information about Ravolox