Eta Canis Majoris
Epoch J2000 Equinox J2000
|Right ascension||07h 24m 05.70228s|
|Declination||–29° 18′ 11.1798″|
|Apparent magnitude (V)||2.450|
|Spectral type||B5 Ia|
|U−B color index||−0.708|
|B−V color index||−0.087|
|Variable type||α Cyg|
|Radial velocity (Rv)||41.1 km/s|
|Proper motion (μ)||RA: −4.14 mas/yr
Dec.: 5.81 mas/yr
|Parallax (π)||1.64 ± 0.40 mas|
|Distance||approx. 2,000 ly
(approx. 600 pc)
|Absolute magnitude (MV)||-7.0|
|Mass||19.19 ± 1.15 M☉|
|Rotational velocity (v sin i)||50 km/s|
Eta Canis Majoris (η Canis Majoris, abbreviated Eta CMa, η CMa), also named Aludra, is a star in the constellation of Canis Major. Since 1943, the spectrum of this star has served as one of the stable anchor points by which other stars are classified.
The traditional name Aludra originates from the Arabic: العذراء al-adhraa 'the virgin'. This star, along with Epsilon Canis Majoris (Adhara), Delta Canis Majoris (Wezen) and Omicron2 Canis Majoris (Thanih al Adzari), were Al ʽAdhārā (العذاري), 'the Virgins'. In 2016, the International Astronomical Union organized a Working Group on Star Names (WGSN) to catalog and standardize proper names for stars. The WGSN's first bulletin of July 2016 included a table of the first two batches of names approved by the WGSN; which included Aludra for this star.
In Chinese, 弧矢 (Hú Shǐ), meaning Bow and Arrow, refers to an asterism consisting of Eta Canis Majoris, Delta Canis Majoris, HD 63032, HD 65456, Omicron Puppis, k Puppis, Epsilon Canis Majoris, Kappa Canis Majoris and Pi Puppis. Consequently, Eta Canis Majoris itself is known as 弧矢二 (Hú Shǐ èr, English: the Second Star of Bow and Arrow.)
Aludra shines brightly in the skies in spite of a large distance from Earth due to being intrinsically many times brighter (absolute magnitude) than the Sun. A blue-white supergiant of spectral type B5Ia, Aludra has a luminosity 176,000 times and a diameter around 80 times that of the Sun. Hohle and colleagues, using the parallax, extinction and analysis of spectrum, came up with a mass 19.19 times that and luminosity 105,442 times that of the Sun. It has only been around a fraction of the time the Sun has, yet is already in the last stages of its life. It is still expanding and may become a red supergiant, or perhaps has already passed that phase, but in either case it will become a supernova within the next few million years.
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- 弧矢 (Hú Shǐ) is westernized into Koo She. R.H. Allen had opinion that Koo She refers to the asterism including Delta Velorum and Omega Velorum. AEEA opinion is, Delta Velorum is member of 天社 (Tiān Shè), meaning Celestial Earth God's Temple asterism and Omega Velorum is not member of any asterisms. 天社 (Tiān Shè) is westernized into Tseen She and R.H.Allen used the term Tseen She for Chinese name of Eta Carinae. See Richard Hinckley Allen: Star Names — Their Lore and Meaning: Argo Navis and (Chinese) AEEA (Activities of Exhibition and Education in Astronomy) 天文教育資訊網 2006 年 7 月 17 日.
- (Chinese) AEEA (Activities of Exhibition and Education in Astronomy) 天文教育資訊網 2006 年 7 月 17 日
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- Watson, Christopher (3 May 2013). "Eta Canis Majoris". AAVSO Website. American Association of Variable Star Observers. Retrieved 5 February 2014.