Astronomy Picture of the Day

Explanation: The Crab Nebula is catalogued as M1, the first on Charles Messier's famous list of things which are not comets. In fact, the Crab is now known to be a supernova remnant, an expanding cloud of debris from the explosion of a massive star. The violent birth of the Crab was witnessed by astronomers in the year 1054. Roughly 10 light-years across today, the nebula is still expanding at a rate of over 1,000 kilometres per second. Flipping between two images made nearly 30 years apart, this animation clearly demonstrates the expansion. The smaller Crab was recorded as a photographic image made in 1973 using the Kitt Peak National Observatory 4-metre telescope in 1973. The expanded Crab was made this year with the Kitt Peak Visitor Centre's 0.4-metre telescope and digital camera. Background stars were used to register the two images.