A supernova remnant approximately 6500 l.y. away in the constellation Taurus; also known as M1 or NGC 1952, and as the radio source Taurus A. The Crab Nebula is the remains of a star that was seen to explode as a supernova of Type II in ad 1054, reaching a maximum apparent magnitude of −6. In telescopes it appears as an elliptical nebulosity of 8th magnitude. Its true dimensions are 11 × 7.5 l.y. Optically, the nebula has two components: an outer region of reddish, twisted filaments of hydrogen gas; and an inner, whitish core that shows no spectral features. The light from the core is synchrotron radiation, caused by high-speed electrons from the Crab Pulsar. It is highly polarized and is continuous at all wavelengths, from gamma rays to radio waves. The expansion velocity of the outer filaments is about 1000 km/s. There is evidence that the expansion is accelerating, driven by the radiation from the pulsar.

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