The
Crab Nebula (catalogue designations
M1,
NGC 1952,
Taurus A) is a
supernova remnant and
pulsar wind nebula in the
constellation of
Taurus. The common name comes from a drawing that somewhat resembled a crab with arms produced by
William Parsons, 3rd Earl of Rosse, in 1842 or 1843 using a 36-inch (91 cm)
telescope.
[6] The
nebula was discovered by English astronomer
John Bevis in 1731. It corresponds with
a bright supernova recorded by
Chinese astronomers in 1054 as a
guest star. The nebula was the first astronomical object identified that corresponds with a historically-observed supernova explosion.
[7]At an
apparent magnitude of 8.4, comparable to that of
Saturn's moon Titan, it is not visible to the naked eye but can be made out using
binoculars under favourable conditions. The nebula lies in the
Perseus Arm of the
Milky Way galaxy, at a distance of about 2.0
kiloparsecs (6,500
ly) from Earth. It has a diameter of 3.4 parsecs (11 ly), corresponding to an apparent diameter of some 7
arcminutes, and is expanding at a rate of about 1,500 kilometres per second (930 mi/s), or 0.5% of the
speed of light.At the center of the nebula lies the
Crab Pulsar, a
neutron star 28–30 kilometres (17–19 mi) across with a spin rate of 30.2 times per second, which emits pulses of
radiation from
gamma rays to
radio waves. At
X-ray and gamma ray
energies above 30
keV, the Crab Nebula is generally the brightest persistent gamma-ray source in the sky, with measured flux extending to above 10
TeV. The nebula's radiation allows detailed study of celestial bodies that
occult it. In the 1950s and 1960s, the Sun's
corona was mapped from observations of the Crab Nebula's radio waves passing through it, and in 2003, the thickness of the atmosphere of Saturn's moon Titan was measured as it blocked out X-rays from the nebula.
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