Wikipedia:Today's featured article/June 14, 2006



The Crab Nebula is a supernova remnant in the constellation of Taurus. The nebula was first observed by John Bevis in 1731, and is the remnant of a supernova that was recorded by Chinese and Arab astronomers in 1054 as being visible during daylight for 23 days. Located at a distance of about 6,300 light years from Earth, it has a diameter of 6 light years and is expanding at a rate of about 1500 kilometres per second. A pulsar in the centre of the nebula rotates 30 times per second, emitting pulses of radiation across the electromagnetic spectrum from radio waves to gamma rays. Its discovery provided the first conclusive evidence that supernova explosions produce the extremely dense neutron stars which are observed as pulsars. The nebula acts as a source of radiation for studying celestial bodies that occult it. The Sun's corona was mapped in the 1950s and 60s from observations of the Crab's radio waves passing through it, and more recently, the thickness of the atmosphere of Saturn's moon Titan was measured as it blocked out X-rays from the nebula. (More...)

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