Alpha Muscae

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**Alpha Muscae**
Observation data Epoch J2000.0
Constellation (pronunciation)	Musca
Right ascension	12^h 37^m 11.08^s
Declination	-69° 08' 07.9"
Apparent magnitude (V)	+2.69
Absolute magnitude (V)	-2.17
Distance	306 ly (93.86 pc)
Spectral type	B2IV-V
Other designations
Myia, HR 4798, HD 109668, CD -68 1104, HIP 61585, SAO 251974, FK5 474, GC 17179

Alpha Muscae (α Mus / α Muscae) is a Class B2, third-magnitude star in the constellation Musca. It is occasionally called by the Greek name Myia, meaning "fly". Since the constellation Musca is a modern constellation that is too far south to have been visible from ancient Greece, this name was given to α Muscae during the modern era, in 1752, when the constellation name "Apis" was changed to "Musca Australis".

This hot class B (B2) subgiant shines from a distance of 306 light years at a luminosity of 4,520 times that of the Sun from a blue-white surface with a fairly well determined temperature of 21,900 kelvins, so hot that most of the radiation emerges in the ultraviolet (where we cannot see it). The combination of temperature and luminosity indicates a radius 4.7 times that of the Sun, and these in conjunction with the theory of stellar structure and stellar evolution tell of an eight solar mass star that is roughly midway through its 32 million year hydrogen-fusing dwarf lifetime (the "subgiant" classification is clearly inappropriate, since subgiants stars tend to give up their core nuclear fusion). Like most class B stars, it rotates quickly, spinning with an equatorial velocity of at least 114 kilometers per second, which gives it a rotation period of less than two days. Also like many stars in its class, Alpha Muscae is a Beta Cephei variable, subtly pulsating in brightness by about one percent over a 2.2 hour period. About half a minute of arc away is a purported 13th magnitude companion, which could also easily be a line-of-sight coincidence. Alpha Muscae is a part of the unbound "Centaurus-Crux" association of O and B type stars, all of which were born more or less at the same time from a massive interstellar cloud.