The Crab Nebula

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Telescope: 40 inch (Siding Spring Observatory) Camera: Wide Field Imager (WFI) Filters: Red Exposure: 3 mins Date: 2005 Where: Siding Spring Observatory, Coonabarabran Lat: 31 16 35.05 S, Long 149 11 33.99 E, Elevation 1148 metres

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Telescope: 14 inch Meade LX200 GPS Camera: SBig ST-8 Filters: BVR Exposure: 40:40:40 Date: 18 November 2006 Processing: Maxim DL, Combine BVR 3:1.5:1, stretch 0.2 gamma, histogram exponential Where: Tenby Observatory, Coonabarabran Lat: 31 16 35.05 S, Long 149 11 33.99 E, Elevation 547 metres

Common Name: The Crab Nebula Other Names: M1 RA: 5 34.5 Dec +22.01 Constellation: Taurus Distance: 6300 light years Magnitude: 8.4 Notes: The Crab Nebula is a supernova remnant. The supernova was observed by the chinese in 1054 and the nebula has been expanding ever since. This supernova was recorded to be visible in the daytime for 23 days and reached a magnitude of -6, i.e. 4 times brighter than planet Venus. The supernova was visible in the night sky for 653 days. There are also records of this event in Mexico but funny enough it seems to be unrecorded in Europe. The nebula was discovered in 1731 by John Bevis in England. It was also recorded by Messier some years later and started of his famous catalogue. He originally thought this object was comet Halley and started the Messier Catalog so astronomers would not confuse these objects for comets. In 1913 Vesto Slipher did spectroscopic studies on the Crab Nebula and noticed the emission lines were split. This indicated that part of the nebula was blue shifted and the other red shifted. In 1919 Roscoe Sanford found there were two kinds of spectra, a continuous spectrum and an emission spectrum. We now know the continuous spectrum is caused by ellectrons being accelerated in a strong magnetic field and the emission spectra comes from the filaments seen in the photo which comes from the outer layers of the star. in 1921 it was discovered that the cloud was expanding by comparing previous photographs. Backtracking it was estimated that the object came into being 900 years earlier. It was then realised that this coincided with the time and position of 'The Guest Star' in 1054. Later observations showed that the expansion started in the 1100s. This means that the expansion must have accelerated. The rate of expansion is 1800km/sec and now the nebula is over 10 light years across. In 1948John Bolton discovered radio waves from this object. X rays were discovered in 1963. Aricebo Observatory in 1968 discovered that the radio source was pulsating at 33 milliseconds. The source of this signal is now known to be a spinning Neutron Star or also called a Pulsar. Pulsars are very dense, more denser than an atomic nucleus. There is more than 1 solar mass in a diameter between 15 and 30 km. Pulsars have very strong magnetic fields which direct jets from the magnetic poles of the pulsar. Its this radiation we observe as pulsating as the pulsar spins. The radiation is about 100 000 times what the sun gives out . The magnetic field is slowing the spin of the pulsar. The magnitude of the pulsar is 16 so has an absolute magnitude of 4.5 in the visible spectrum, same as the sun.