Crab nebula (M1, upper right) and the star Zeta Tauri (lower left). The Crab nebula is a supernova remnant, expanding shells of gas cast off by a supernova, the explosive death of a massive star. The Crab nebula is notable as its explosion was recorded by Chinese and Arab astronomers in 1054 AD, when it appeared as a new star, which was visible in daylight and faded slowly over two years before becoming invisible to the naked eye. The supernova remnant itself was discovered in 1731, although it takes its M1 classification from its later discovery by Charles Messier in 1758, when he gave it the first number in his catalogue of objects. Photographed by the 1.22 metres Oschin Telescope, Mount Palomar, California, USA.