Mu Cephei.html



Mu Cephei (μ Cep / μ Cephei), also known as Herschel's Garnet Star, is a Red supergiant star in the constellation Cepheus. It is one of the largest and most luminous stars known in the Milky Way. It appears garnet red due to its spectral class of M2Ia.

History

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The deep red colour of Mu Cephei was noted by William Herschel, who noted one star which was "a very fine deep garnet colour, such as the periodical star ο ceti" in the 1783 edition of the Philosophical Transactions,^{citation needed} and it is thus commonly known as "Herschel's Garnet Star". Giuseppe Piazzi called it Garnet Sidus in his Palermo Catalogue of stars.^{citation needed}

An alternative name Erakis, used in Antonín Bečvář's star catalogue is probably due to confusion with Mu Draconis, which was previously called al-Rāqis ar-rá:qis in Arabic.^{citation needed}

Properties

A very luminous red supergiant, Mu Cephei is one of the largest and brightest stars visible not only to the naked eye but in the entire Galaxy. It is best seen from the Northern hemisphere from August to January.

The star is approximately 1,420 times larger than our sun's solar radius, and if it were placed in the Sun's position, its radius would reach between the orbits of Jupiter and Saturn. Mu Cephei could fit over 1 billion suns into its body. Only five known stars (VY Canis Majoris, KW Sagitarii, KY Cygni, V354 Cephei and VV Cephei) are believed to be larger than it. It is so large that it could fit 3 trillion Earths in it. If Earth were a golf ball, that would be enough golf balls to fill up the superdome--3,000 times.

Mu Cephei is a variable star and the prototype of the class of the Mu Cephei variables. Its apparent brightness varies without recognizable pattern between +3.62 mag and +5 mag in a period of 2 to 2.5 years. Mu Cephei is 38,000 times brighter than the Sun, with an absolute visible magnitude of M_v = −7.0. Combining its absolute visible brightness, its infrared radiation and its interstellar extinction gives a luminosity of around 350,000 solar luminosities, making it one of the most luminous stars known. Its distance is not very well known. Parallax measurements or distance estimates in the scientific literature give values between 390 and 1,600 parsecs (1,300 and 5,200 ly).¹

Mu Cephei is now in the dying stage of stars. It has begun to fuse helium into carbon, whereas a "healthy" main sequence star fuses hydrogen into helium. The helium-carbon cycle shows that Mu Cephei is in the last phase of its life and is possibly about to go supernova (in astronomical terms, of course: at least some million years). When a star goes supernova it is destroyed, leaving behind a vast hydrogen cloud which, for a star as massive as Mu Cephei, may be centered on a black hole.

See also

• IC 1396
• List of largest stars
• List of most luminous stars

References

• image Mu Cephei
• http://jumk.de/astronomie/big-stars/garnet-star.shtml

External links

• "HD 206936". SIMBAD. Retrieved on 13 April 2006.
• The Garnet Star from Jim Kaler's Stars.
• AAVSO: Star of the Month from AAVSO: Variable Star of the Month, Mu Cephei
• Mu Cephei a grand red star
• My Cephei imaged with a semiprofessional telescope in an amateur-observatory