Crab Nebula

The Crab Nebula (also known as Messier Object 1, M1 or NGC 1952) is a gaseous diffuse nebula in the constellation Taurus. It 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 6500 ly from Earth, it has a diameter of 6 ly and is expanding at a rate of 1000 km per second. A neutron star in the center of the nebula rotates 30 times per second.

General information

The Crab Nebula is often used as a calibration source in X-ray astronomy.

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It is very bright in X-rays and the flux density and spectrum are known to be constant, with the exception of the pulsar.

Related Topics:
X-ray - Flux density - Spectrum

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The pulsar provides a strong periodic signal that is used to check the timing of the X-ray detectors. In X-ray astronomy, 'Crab' and 'milliCrab' are sometimes used as units of flux density. Very few X-ray sources ever exceed one Crab in brightness.

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The Crab Nebula derived its name from its appearance in a drawing made by Lord Rosse in 1844 using his 36-inch telescope. In this sketch it does indeed resemble a crab, but upon reobserving the nebula in 1848 with his newly-built 72-inch telescope he produced a much more accurate drawing which bore little resemblance to the original. However, the name "Crab Nebula" stuck.

Related Topics:
Lord Rosse - 1844 - 1848

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