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The '''Crab Nebula''', also known as '''M1''' and '''NGC 1952''', is an expanding gas cloud surrounding a [[neutron star]] located in the constellation of [[Taurus]] near the star [[Zeta Tauri]], the south horn of the bull. Possibly the most famous [[nebula]], it is the result of a [[supernova]] event that was first observed on [[Earth]] in 1054 A.D.  Since then, the nebula has been expanding at a rate of 1500&nbsp;km/s and is now on average some 11 light years in diameter.<ref>http://apod.nasa.gov/apod/ap011227.html</ref>

The '''Crab Nebula''', also known as '''M1''' and '''NGC 1952''', is an expanding gas cloud surrounding a [[neutron star]] located in the constellation of [[Taurus]] near the star [[Zeta Tauri]], the south horn of the bull. Possibly the most famous [[nebula]], it is the result of a [[supernova]] event that was first observed on [[Earth]] in 1054 A.D.  Since then, the nebula has been expanding at a rate of 1,500&nbsp;km/s and is now on average some 11 light years in diameter.<ref>[http://apod.nasa.gov/apod/ap011227.html The Incredible Expanding Crab] from [[NASA]]'s Astronomy Picture of the Day</ref>

==Supernova Event==

==Supernova Event==

The Crab Nebula is the result of the supernova event called '''SN1054''', which was first recorded by [[Chinese]] and [[Arab]] astronomers on July 4, 1054 A.D. as a "guest star".  The event was possibly also the inspiration for astronomy-related art created by [[Anasazi]] [[Indians]].<ref>http://www.astronomy.pomona.edu/archeo/outside/chaco/nebula.html</ref> Initially the supernova had an apparent magnitude of -6, making it brighter then even [[Venus]]. The star then began to fade, but remained subsequently bright enough to be observed during the day for the next 23 days, and at night for the next 653 days before finally fading from view.<ref>http://www.seds.org/messier/more/m001_sn.html</ref> The supernova has been classified since with the variable star designation '''CM Tauri'''.  

The Crab Nebula is the result of the supernova event called '''SN 1054''', which was first recorded by [[Chinese]] and [[Arab]] astronomers on July 4, 1054 A.D. as a "guest star".  The event was possibly also the inspiration for astronomy-related art created by [[Anasazi]] [[Indians]].<ref>[http://www.astronomy.pomona.edu/archeo/outside/chaco/nebula.html Chaco: 1054 Supernova Petrograph] from astronomy.pomona.edu</ref> Initially the supernova had an apparent magnitude of -6, making it brighter then even [[Venus]]. The star then began to fade, but remained subsequently bright enough to be observed during the day for the next 23 days, and at night for the next 653 days before finally fading from view.<ref>[http://www.messier.seds.org/m/m001.html Messier 1] from messier.seds.org</ref> The supernova has been classified since with the [[variable star]] designation '''CM Tauri'''.  

Based on theoretical models of supernova explosions, the progenitor star for the explosion is calculated to have been between 9 and 11 solar masses.<ref>http://adsabs.harvard.edu/abs/1985cnrs.work...97N</ref>

Based on theoretical models of supernova explosions, the progenitor star for the explosion is calculated to have been between 9 and 11 [[solar mass]]es.<ref>Nomoto, K. (1985). Evolutionary models of the Crab Nebula's progenitor. In: ''The Crab Nebula and related supernova remnants; Proceedings of the Workshop.'' [online] Cambridge and New York: Cambridge University Press, pp.97-113. Available [http://adsabs.harvard.edu/abs/1985cnrs.work...97N Online] [Accessed 10 May 2018].</ref>

==History of Observation==

==History of Observation==

[[Image:CrabNebula.jpg|thumb|left|250px|This image from the Chandra X-Ray Observatory shows the central pulsar of the Crab Nebula surrounded by tilted rings of high-energy particles.]]

[[Image:CrabNebula.jpg|thumb|left|250px|This image from the [[Chandra|Chandra X-Ray Observatory]] shows the central [[pulsar]] of the Crab Nebula surrounded by tilted rings of high-energy particles.]]

The first person to discover the nebula remnant was [[English]] astronomer [[John Bevis]] in 1731, who recorded it in his book, ''Uranographia Britannica''.  Later in 1758, [[Charles Messier]] discovered the nebula independently while he was searching for [[Halley's Comet]], and initially mistook the nebula for another [[comet]].  He soon realized it wasn't, when it became apparent it lacked any proper motion, and it became the first astronomical object recorded in his famous ''Catalogue des Nébuleuses et des Amas d'Étoiles'' ("Catalogue of Nebulae and Star Clusters").

The first person to discover the nebula remnant was [[English]] astronomer [[John Bevis]] in 1731, who recorded it in his book, ''Uranographia Britannica''.  Later in 1758, [[Charles Messier]] discovered the nebula independently while he was searching for [[Halley's Comet]], and initially mistook the nebula for another [[comet]].  He soon realized it wasn't, when it became apparent it lacked any proper motion, and it became the first astronomical object recorded in his famous ''Catalogue des Nébuleuses et des Amas d'Étoiles'' ("Catalogue of Nebulae and Star Clusters").

The name "Crab Nebula" itself originated from a drawing of the nebula made by '''Lord Rosse''' in 1844, where the supernova remnant looked like a crab.<ref>http://seds.org/MESSIER/more/m001_rosse.html</ref>

The name "Crab Nebula" itself originated from a drawing of the nebula made by '''Lord Rosse''' in 1844, where the supernova remnant looked like a crab.<ref>[http://www.messier.seds.org/more/m001_rosse.html Lord Rosse's drawings of M1, the Crab Nebula] from messier.seds.org</ref>

In 1892 the first [[photograph]] was taken of the nebula using a 20-inch [[telescope]].  Later in 1921 it was discovered that the nebula was expanding at a rate that allowed for the tracing of its origin to about 900 years before.<ref>http://adsabs.harvard.edu/abs/1921PNAS....7..179D</ref>  In the same year it was independently realized that the nebula was in the proximity of the supernova SN1054.  These two observations led to the revelation that the nebula was the remnant of that same supernova event.<ref>http://adsabs.harvard.edu/abs/1921PASP...33..225L</ref>

In 1892 the first [[photograph]] was taken of the nebula using a 20-inch [[telescope]].  Later in 1921 it was discovered that the nebula was expanding at a rate that allowed for the tracing of its origin to about 900 years before.<ref>Duncan, J. (1921). Changes Observed in the Crab Nebula in Taurus. ''Proceedings of the National Academy of Sciences'', 7(6), pp.179-180.1. [http://adsabs.harvard.edu/abs/1921PNAS....7..179D Online]</ref>  In the same year it was independently realized that the nebula was in the proximity of the supernova SN&nbsp;1054.  These two observations led to the revelation that the nebula was the remnant of that same supernova event.<ref>Lundmark, K. (1921). Suspected New Stars Recorded in Old Chronicles and Among Recent Meridian Observations. ''Publications of the Astronomical Society of the Pacific'', 33(195), p.225. [http://adsabs.harvard.edu/abs/1921PASP...33..225L Online]</ref>

Later in 1949, the nebula was discovered to be a strong source of [[radio waves]].<ref>http://adsabs.harvard.edu/abs/1949Natur.164..101B</ref>  In 1963 it was discovered that the nebula was also a major source of [[x-rays|x-ray]], emitting x-ray [[radiation]] at 100 times the energy the nebula emits energy in the visual spectrum.<ref>http://www.sciencemag.org/cgi/content/abstract/146/3646/912</ref> Eventually the source of this energy was discovered in 1968, when a radio [[pulsar]], later revealed to be a neutron star, was found.

Later in 1949, the nebula was discovered to be a strong source of [[radio waves]].<ref>BOLTON, J., STANLEY, G. and SLEE, O. (1949). Positions of Three Discrete Sources of Galactic Radio-Frequency Radiation. ''Nature'', 164(4159), pp.101-102. [http://adsabs.harvard.edu/abs/1949Natur.164..101B Online]</ref>  In 1963 it was discovered that the nebula was also a major source of [[x-rays|x-ray]], emitting x-ray [[radiation]] at 100 times the energy the nebula emits energy in the visual spectrum.<ref>[http://www.sciencemag.org/cgi/content/abstract/146/3646/912 Lunar Occultation of X-ray Emission from the Crab Nebula] from sciencemag.org</ref> Eventually the source of this energy was discovered in 1968, when a radio [[pulsar]], later revealed to be a [[neutron star]], was found.

==Properties==

==Properties==

Despite being one of the best known nebulae, the Crab Nebula is invisible to the unaided eye, with an apparent magnitude of only +8.4  The exact distance of the nebula itself is unknown. It is roughly 11 light years across overall, extending some 13 light years across at its longest.  Right now the nebula's gasses are expanding at around 1500&nbsp;km/s, and it is believed that this velocity is increasing due to energy emitted from the pulsar. The amount of matter in the nebula is estimated to be around 4.6 ± 1.8 solar masses, and is used to help estimate the total mass of the progenitor star.<ref>http://adsabs.harvard.edu/abs/1997AJ....113..354F</ref>

Despite being one of the best known nebulae, the Crab Nebula is invisible to the unaided eye, with an apparent magnitude of only +8.4  The exact distance of the nebula itself is unknown. It is roughly 11 light years across overall, extending some 13 light years across at its longest.  Right now the nebula's gasses are expanding at around 1,500&nbsp;km/s, and it is believed that this velocity is increasing due to energy emitted from the pulsar. The amount of matter in the nebula is estimated to be around 4.6 ± 1.8 solar masses, and is used to help estimate the total mass of the progenitor star.<ref>Fesen, R., Shull, J. and Hurford, A. (1997). An Optical Study of the Circumstellar Environment Around the Crab Nebula. ''The Astronomical Journal'', 113, p.354-363. [http://adsabs.harvard.edu/abs/1997AJ....113..354F Online]</ref>

===Crab Pulsar===

===Crab Pulsar===

The '''Crab Pulsar''' is a rapidly rotating [[neutron star]] some 28-30 kilometers in diameter, and has a mass twice that of the [[Sun]].<ref>http://adsabs.harvard.edu/abs/2002A%26A...396..917B</ref>  The pulsar rotates once every 33 milliseconds, emitting radiation towards us once per rotation.  This allows us to measure its rotational speed at 6.4 million km/h.  The pulsar is slowing down though, rotating 15 microseconds slower each year.  The [[radiation]] emitted though from the remnant pulsar is enough to illuminate the entire Crab Nebula with a total luminosity some 75,000 time greater than our Sun.<ref>http://www.solstation.com/x-objects/crab-neb.htm</ref>

The '''Crab Pulsar''' is a rapidly rotating [[neutron star]] some 28-30 kilometers in diameter, and has a mass twice that of the [[Sun]].<ref>Bejger, M. and Haensel, P. (2002). Moments of inertia for neutron and strange stars: Limits derived for the Crab pulsar. ''Astronomy & Astrophysics'', 396(3), pp.917-921. [http://adsabs.harvard.edu/abs/2002A%26A...396..917B Online]</ref>  The pulsar rotates once every 33 milliseconds, emitting radiation towards us once per rotation.  This allows us to measure its rotational speed at 6.4 million km/h.  The pulsar is slowing down though, rotating 15 microseconds slower each year.  The [[radiation]] emitted though from the remnant pulsar is enough to illuminate the entire Crab Nebula with a total luminosity some 75,000 time greater than our Sun.<ref>[http://www.solstation.com/x-objects/crab-neb.htm Crab Nebula & Pulsar] from solstation.com</ref>

 

==References==

==References==