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Betelgeuse, also called α Orionis, is a red supergiant star in the constellation of Orion. It is the 10th brightest star in the sky, and is a vertex of the Winter Triangle. Its proximity to Earth combined with its enormous size make it (aside from the Sun) the largest star as viewed from Earth, and the only star that current telescopes can resolve to a visible disk. (See photo.)

Even though it is the α star of Orion, it is not the brightest. Rigel, also known as β Orionis, is actually brighter.

Origin of the name "Betelgeuse"

The name is a corruption of the Arabic Yad al-Jauza`, translated as the "hand of the central one". Jauza`, the central one, initially referred to Gemini among the Arabs, but at some point they decided to also refer to Orion by that name. During the Middle Ages the first character of the name was misread when transliterating into Latin, and Yad al-Jauza` became Bedalgeuze. Then, during the Renaissance, someone tried to derive the original Arabic from this corrupted name, and decided that it was originally written as Bait al-Jauza`. This imaginative person then declared that Bait meant "armpit" in Arabic, to the surprise of Arabs everywhere. The nameless Renaissance linguist then "corrected" the transliterated spelling to Betelgeuse, and the modern rendering was born.

In order for Betelgeuse to really mean "armpit of the central one", the original rendering would have to have been Ibt al-Jauza`.

Observation Data
Epoch J2000
Variability SR c (Semiregular Variable)
Spectral Type M1-2 Ia-Iab (Red Super Giant)
Right Ascension 05h 55m 10.29s
Declination +07° 24′ 25.3″
Distance 427 ± 92 ly (131 pc)
Apparent Magnitude (V) +0.45 (+0.3 to +0.6 (+1.3))
Physical Characteristics
Mass 40 × 1030 kg (~20 M)
Radius 190 million km (273 R)
Colour (B-V) +1.850 (Orange-red)
Colour (V-I) 2.32
Absolute Magnitude (V) -5.3 to -5.0
Luminosity (V) 10,000 L
Surface Temperature 3600 K
Rotation Period
Oscillation Period ~ 2070 d to 2355 d
Notable Features
Other Designations
Stellar Components
Stellar Companions
Planets and Minor Bodies

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. Other names are:

  • Al Dhira (the Arm),
  • Al Mankib (the Shoulder)
  • Al Yad al Yamma (the Right Hand)
  • Ardra (Hindi),
  • 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

Distinguishing characteristics

Betelgeuse is of great interest astronomically. It is 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. Though only 20 times as massive as the Sun, it is as much as 40 million times larger in volume, like a beach ball compared to Texas Stadium.

Astronomers confidently predict that Betelgeuse will ultimately undergo a type II supernova explosion. Opinions are divided as to the likely timescale for this event. Some regard the star's current variability as suggesting that it is already in the carbon burning phase of its life cycle, and will therefore go supernova at some time in the next thousand years or so. Skeptics dispute this contention and regard the star as being likely to survive much longer. There is a consensus that such a supernova would be a spectacular astronomical event, but would not represent any significant threat to life on Earth given the star's enormous distance.

References in fiction

In science fiction, Ford Prefect, a character in the Hitchhiker's Guide to the Galaxy, hails from a world "in the vicinity of Betelgeuse".

Betelgeuse is also the name of the main character of the 1988 comedy/fantasy film Beetlejuice.

Last updated: 02-07-2005 18:09:57
Last updated: 05-03-2005 02:30:17