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Betelgeuse, also called α Orionis, is a large red star in the constellation of Orion. It is the 12th brightest star in the sky, a red giant, and is a vertex of the Winter Triangle.

The name is a contraction of the Arabic Yad al-Jauza`, translated as the "armpit of the central one," indicating its position in the constellation of Orion. Because of its rich reddish color the star has frequently been referred to as the "martial one," and in Astrology portends military or civic honors. Because it is the first star of Orion to rise, the title of "roarer" or "announcer" has been assigned to it by ancient writers. Other names are:

  • Al Dhira (the Arm),
  • Al Mankib (the Shoulder)
  • Al Yad al Yamma (the Right Hand)
  • Ardra (Hindu),
  • Bahu (Sanskrit),
  • Bed Elgueze
  • Beit Algueze
  • Besn (Persian) (the Arm),
  • Beteigeuze
  • Beteiguex
  • Betelgeuze(Bet El-geuze),
  • Betelgeza (Slovene),
  • Betelguex
  • Gula (Euphratean),
  • Ied Algeuze (Orion's Hand),
  • Klaria (Coptic) (an Armlet)
  • Yedelgeuse

Physical and other characteristics

Observation data
Semiregular Variable, type SR c  
Right ascension (RA, α) (J2000,00) 05 h 55 m 10.29 s
Declination (Dec, δ) (J2000,00) +07° 24' 25.3"
Distance from Earth 427 ± 92 LY (131 pc)
Visual brightness (V)  +0.45m (+0.3m to +0.6m (+1.3m))
Absolute magnitude -5.3m to -5.0m 
Physical characteristics
Mean Diameter (dS = 1,392,000 km) 385,000,000 km | ~ 276.6 dS
2.57 AU | (452 s.u.)
Surface area  
Mass ~ 40 × 1030 kg
Relative mass to the Sun
(mS = 1.9891 × 1030 kg)
~ 20 mS
Surface gravity  
Spectral type M1-2 Ia-Iab (Red Super Giant)
Surface temperature 3600 K
Color (B-V) +1.850 (Orange-red) | (1.500)  
V-I 2.32
Luminosity (LS = 3.827 × 1026 J s-1) ~ 10,000 LS
Orbital characteristics
Period of rotation 
Period ~ 2070 d to 2355 d

Betelgeuse is of great interest astronomically. It is also one of the first stars to have its diameter measured with a stellar interferometer. The diameter was found to be variable, ranging from 290,000,000 km to 480,000,000 km. At maximum diameter, the star would extend out beyond the orbit of Mars if put in the Sun's place.

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