Crab Nebula

The Crab Nebula was a nebula which the First Doctor believed to be outside of Mutter's Spiral. (PROSE: The Sons of the Crab)

Features
The planet Wengrol was located in the Crab Nebula, (PROSE: The Sons of the Crab) as was the planet Tora. (COMIC: The Enlightenment of Ly-Chee the Wise)

The planet Yamado was located near the Crab Nebula. (COMIC: K-9's Finest Hour)

History
The Crab Nebula was created by the Uxarieans by detonating a star with their Doomsday Weapon. (TV: Colony in Space) This was believed to have occurred during the Millennium War circa 150 million BC. (PROSE: The Quantum Archangel)

During a visit to 1980s Blackpool, the Sixth Doctor said that a replica of the town was being built on the rim of the Crab Nebula, but they had gotten the design concept wrong, as it was being built for a purpose rather than for frivolity. (PROSE: The Nightmare Fair, AUDIO: The Nightmare Fair)

From the late 23rd century to around 2399, the Bathory outpost was located in the Crab Nebula. (PROSE: Iris at the V&A)

In the 51st century, humanity relocated to the Crab Nebula after Earth was ruined by solar flares. (COMIC: The Keep)

Undated events
Operating from Yamado on behalf of the Sontarans, Firandel and Rolgot used a gravatronic tractor beam to capture the Doctor's TARDIS in the nearby Crab Nebula, but accidentally locked on to K9 Mark II instead of the Fourth Doctor, kidnapping the robot. K9 realised their intention to kidnap and kill the Doctor because of the lack of air on his expected arrival and overpowered his "hosts" before the Doctor and the TARDIS arrived in safety to collect him. (COMIC: K-9's Finest Hour)

The Tenth Doctor once took Grayla to either the Crab Nebula or the Horsehead Nebula. (COMIC: The Whispering Gallery)

Behind the scenes
In the real world, the Crab nebula is a supernova remnant in the Perseus arm of the Milky Way Galaxy. In The Sons of the Crab, the First Doctor believes the nebula to be outside of the Milky Way, however, and there is currently no other evidence cited on this page related to its location in-universe.