Andromeda (galaxy)

The Andromeda Galaxy, also referred to as Messier Object 31, M31, or NGC 224, is a massive spiral galaxy in the Local Group, together with Mutter's Spiral and thirty-one other galaxies. Andromeda is approximately 2.9 million light-years, or 920  kiloparsecs, from Earth's galaxy. ''

Andromeda is much larger and possibly more massive than Earth's galaxy, indicating that it should contain substantially more stars and thus, planets. However, the Doctor and his companions appear to have visited only a handful of planets in that galaxy. Doctor Who chronology has humans reaching Andromeda sometime after the 50th century.

Doctor Who story notes

 * The Wirrn are native to Andromeda, their nesting grounds being destroyed by human colonists and a lone surviving Queen fleeing that galaxy thousands of years before the events of "The Ark in Space."


 * The town of Castrovalva, a block transfer computation structure created by the Master as a trap for the Fifth Doctor, was located on a lush green world in Andromeda.


 * In its background information for the Movellans, the FASA role-playing game described the android race as having originated in Andromeda, before being expelled from that galaxy by a coalition of races known as the Organic League.


 * In The Trial of a Time Lord, we discover that an agency known as 'the Three Sleepers' originate from Andromeda. Having stolen data from the Matrix on Gallifrey, the Sleepers took refuge on Earth of the far future; in retribution, the Time Lords used their Magnetron to devastate the planet by fire, moving it two light years to cover up the leak. Owing to the move a rescue ship sent from Andromeda to recover the Sleepers, and the data, missed Earth and the Sleepers died in suspended animation. In the same story, Sabalom Glitz is said to be 'from the constellation of Andromeda'.

For detailed real world information on the Andromeda Galaxy see the Wikipedia article on that topic.