Missing image
Hubble UV picture of Betelgeuse. Ground-based instruments can produce images with higher resolution than Hubble for bright stars such as Betelgeuse.

Betelgeuse (α Ori / α Orionis / Alpha Orionis) is the second brightest star in the constellation Orion and the tenth brightest star in the nighttime sky. Although it has the Bayer designation "alpha", it is not as bright as Rigel (Beta Orionis).

Betelgeuse is vertex of the Winter Triangle.

Betelgeuse is a red supergiant star, one of the physically largest stars known. If it was placed at the center of our Solar System, the Earth would be engulfed and would be inside it. Its proximity to Earth combined with its enormous size make it the star with the third largest angular diameter as viewed from Earth [1] (, smaller only than the Sun and R Doradus, and one of only a dozen or so stars that telescopes can image as a visible disk as of 2005. (See photo, at right and a picture of hotspots ( on Betelgeuse). The angular diameter of Betelgeuse was first measured in 1920-1921 by Michelson and Pease using an interferometer on the Mount Wilson 100-inch telescope.

Because Rigel is a blue star and Betelgeuse is a red star, Betelgeuse is actually brighter than Rigel at infrared wavelengths, but not at visual wavelengths.


Origin of the name "Betelgeuse"


Missing image
The position of Betelgeuse in the constellation of Orion

The name is a corruption of the Arabic يد الجوزا yad al-jawzā, or "hand of the central one". Jauza, the central one, initially referred to Gemini among the Arabs, but at some point they decided to refer to Orion by that name. During the Middle Ages the first character of the name, y (, with two dots under it), was misread as a b (, with one dot under it) 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 have meant "armpit of the central one", the original rendering would have to have been ابط Ibţ (al-Jauza).

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

Several features of Betelgeuse are of particular interest to astronomers. It was one of the first stars to have its diameter measured with a stellar interferometer; the diameter was found to be variable, ranging from 180 million miles (290,000,000 km) to 300 million miles (480,000,000 km). At maximum diameter, the star would extend out beyond the orbit of Mars if placed at the location of the Sun. Though only 15 times more massive than the Sun, it is as much as 40 million times greater in volume; a difference much like a beach ball compared to Texas Stadium. It was also the first star to have its disk resolved in an optical image by a telescope, from observations by the COAST telescope in 1995 (

Missing image
Artist's impression of Betelgeuse appearing as a supernova above the OWL telescope

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 undergo a supernova explosion 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.

Even so, Betelgeuse would brighten at least 10,000 times as a supernova, causing it to shine with the luminosity of a crescent Moon. Some sources predict a maximum apparent magnitude equal to about that of the full Moon (mv = -12.5). This would likely last for several months. It would look like a brilliant point, the brightness of a full Moon with the color of an incandescent bulb at night, and easily visible in daylight. After that period the star will gradually diminish until after some months or years the star completely disappears, and Orion's left shoulder vanishes.

External links

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 de:Beteigeuze es:Betelgeuse eo:Betelĝuzo fr:Btelgeuse io:Betelgeuse it:Betelgeuse nl:Betelgeuze ja:ベテルギウス no:Betelgeuse pl:Betelgeza pt:Betelgeuse sr:Бетелгез fi:Betelgeuze sv:Betelgeuse zh:參宿四


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