Many people have heard of Hawking radiation, which is a form of radiation emitted by a black hole. Less familiar is Unruh radiation, named after Bill Unruh who first described it. It also is emitted by black holes. Close to a black hole, the radiation is predominantly Unruh; further away, it is predominantly Hawking. Unruh radiation is observed by a detector when it is placed in a state of uniform acceleration, whereas if the same detector is at rest or in a state of uniform motion, no radiation is observed. The Unruh radiation in the case of uniform acceleration is like a black body with a temperature proportional to the acceleration. The relevance to black holes is that, close to a black hole, the geometry of a spherical black hole can be transformed so that it looks like that of a uniformly accelerated object. John Bell suggested that Unruh radiation might be observed in an electron storage ring.