Betelgeuse
Betelgeuse (Alpha (α) Orionis) is a semiregular variable star located 427 light-years away [1]. It is the second brightest star in the constellation Orion, and the tenth brightest star in the night sky. Although it has the Bayer designation "alpha", it is not as bright as Rigel (Beta Orionis). It is a vertex of the Winter Triangle asterism.
Betelgeuse is a red supergiant, one of the physically largest stars known. If it was placed at the center of our solar system, its outer surface would extend well beyond the orbit of the Earth. As it is, Betelgeuse is so large and so close that it is the star with the third largest angular diameter as viewed from Earth [2], smaller only than the Sun and R Doradus, and one of only a dozen or so stars that telescopes have imaged as a visible disk. (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.
Origin of the name "Betelgeuse"
| Observation data Epoch J2000 Equinox J2000 | |
|---|---|
| Constellation | Orion |
| Right ascension | 05h 55m 10.3s |
| Declination | +07° 24' 25" |
| Apparent magnitude (V) | 0.45 |
| Characteristics | |
| Spectral type | M1-2 Ia-Iab |
| U−B color index | 2.06 |
| B−V color index | 1.85 |
| Variable type | SR c (Semi-regular) |
| Astrometry | |
| Radial velocity (Rv) | +21 km/s |
| Proper motion (μ) | RA: 27.33 mas/yr Dec.: 10.86 mas/yr |
| Parallax (π) | 7.63 ± 1.64 mas |
| Distance | 427 ly (131 pc) |
| Absolute magnitude (MV) | -5.14 |
| Details | |
| Mass | 12-17 M☉ |
| Radius | 650 R☉ |
| Luminosity | 9,400 L☉ |
| Temperature | 3,100 K |
| Metallicity | ? |
| Rotation | ? |
| Age | 6 × 106 years |
| Other designations | |
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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 (ﻴ, with two dots under it), was misread as a b (ﺒ, with one dot under it) when transliterating into Latin, and Yad al-Jauza became Bedalgeuze. Then, during the Renaissance, it was thought the name was originally written as Bait al-Jauza or "armpit" in Arabic. This led to the modern rendering as "Betelgeuse". 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, and name of Hindu Nakshatra),
- Bahu (Sanskrit),
- Besn (Persian) (the Arm),
- 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 290,000,000 km (180 million miles) to 480,000,000 km (300 million miles). 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 in volume much like a beach ball compared to Texas Stadium. It was also the first star to have starspots on its disk resolved in optical images by a telescope, first from Aperture Masking Interferometry and later from more detailed observations by the COAST telescope.
Astronomers predict that Betelgeuse will ultimately undergo a type II supernova explosion although it is possible that the mass is low enough for Betelgeuse to leave a rare oxygen-neon white dwarf. 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 – being so distant – represent any significant threat to life on Earth. Indeed, its distance means that a supernova may have already actually occurred but the light from the explosion has not yet reached Earth.
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 it would gradually diminish until after some months or years it would disappear from naked eye view, and Orion's left shoulder would vanish, and in a few centuries become a splendid nebula. However, if Betegeuse's axis (one of its poles) is pointed towards Earth there would be tangible effects here. A shower of gamma rays and other cosmic particles would be directed at Earth. There would be spectacular aurorae and possibly a measurable diminution of the ozone layer with consequent adverse radiation effects on life. In such an orientation towards the solar system it would also appear many times brighter than if its axis were pointed away.
External links
- ^ Images of hotspots on the surface of Betelgeuse taken at visible and infra-red wavelengths using high resolution ground-based interferometers.
- "SIMBAD Query Result for Betelgeuse". SIMBAD international database. April 4.
{{cite web}}: Check date values in:|date=and|year=/|date=mismatch (help) - "Betelgeuse". SolStation. November 11.
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References in fiction
- Tharg the Mighty, the (fictional) editor of the British comic anthology 2000AD since 1978, hails from Betelgeuse, along with his sister Marg. A rudimentary Betelgeusian vocabulary has been developed in the comic.
- In science fiction, Ford Prefect, a character in the Douglas Adams' Hitchhiker's Guide to the Galaxy, hails from "a small planet somewhere in the vicinity of Betelgeuse".
- Betelgeuse is also the name of the main character of the 1988 comedy/fantasy film Beetlejuice.
- In August Derleth's take on H.P. Lovecraft's Cthulhu mythos, Betelgeuse is the home of the 'benign' Elder Gods.
- In Calculating God, a science-fiction novel by Robert J. Sawyer, Betelgeuse becomes a supernova, threatening all life within several hundred light-years. The novel assumes that the gamma ray flux from the supernova is many times that currently estimated by astronomers.
- In Kurt Vonnegut's The Sirens of Titan, Winston Niles Rumfoord has fallen into a spatial phenomenon known as the chronosynclastic infundibulum and has become "one node of a wave phenomenon extending all the way from the Sun to Betelgeuse."
- In Pierre Boulle's novel Planet of the Apes, the planet upon which the majority of the story takes place orbits Betelgeuse.
- In Star Control 2 Betelgeuse (although presumabely in all different place) is also the star upon which the second homeworld of the Syreen orbits.