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Betelgeuse

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)	+0.45^m (+0.3^m to +0.6^m (+1.3^m))
Absolute magnitude	-5.3^m to -5.0^m
Physical characteristics
Mean Diameter (d_S= 1,392,000 km)	385,000,000 km \| ~ 276.6 d_S 2.57 AU \| (452 s.u.)
Surface area
Volume
Mass	~ 40 × 10³⁰ kg
Relative mass to the Sun (m_S= 1.9891 × 10³⁰ kg)	~ 20 m_S
Density
Surface gravity
Spectral type	M1-2 Ia-Iab (Red Super Giant)
Surface temperature	3600 K
Age
Color (B-V)	+1.850 (Orange-red) \| (1.500)
V-I	2.32
Luminosity (L_S = 3.827 × 10²⁶ J s^-1)	~ 10,000 L_S
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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