Supernova A supernova is a STAR that explodes. It suddenly increases in brightness by a factor of many billions, and within a few weeks it slowly fades. In terms of the human lifespan, such explosions are rare occurrences. In our Milky Way galaxy, for example, a supernova may be observed every few hundred years. Three such explosions are recorded in history: in 1054, in 1572, and in 1604. The CRAB NEBULA consists of material ejected by the supernova of 1054. Such materials, known as supernova remnants, are common in the heavens. The supernovas observed in modern times have all occurred in other galaxies, the most distant yet having been detected in 1988 in a galaxy 5 billion light-year