|Astronomical designation||Alpha Orionis|
|Right ascension||05h 55m 10.3053s|
|Declination||+07o 24′ 25.426|
|Type of object||Supergiant star|
|Magnitude||Apparent Mag: 0.58 (0.3 to 1.2)|
Absolute Mag: -5.14
|Distance from Earth||640 ± 140 ly|
|Radial Velocity||+21.0 km/s|
|Proper Motion||RA: 24.95 ± 0.08 mas/yr|
Dec.: 9.56 ± 0.15 mas/yr
|Parallax||5.07 ± 1.10 mas|
Betelgeuse, or Alpha Orionis is an orange-reddish star located in the northeast part the constellation Orion. The star is typically the second brightest in the constellation, although as a variable star, its apparent magnitude can exceed from time to time, that of Rigel, normally the brightest star of Orion.
The name Betelgeuse itself is a corruption of the Arabic يد الجوزاء yad al-jawzā ("hand of the central one"). Other names various Arabic authors have given the star are Al Mankib, (the Shoulder); Al Dhira, (the Arm); and Al Yad al Yamma, (the Right Hand). As one of the most recognizable stars in the night sky, it has many other names throughout the world including Ardra in Hindi, Klaria, meaning an Armlet in Coptic, Bašn meaning the Arm in Persian, and Shēnsùsì (参宿四, the Fourth Star of the Constellation of Three Stars), in Chinese.
Betelgeuse is a luminous red supergiant of spectral and luminosity type M1-2 Ib, with a surface temperature of around 3650 K. The star has an "average" apparent magnitude of 0.58 in the night sky, making it the 9th brightest star. Being a variable star, its magnitude varies between 0.3 and 1.1 over multiple periods in cycles of variability which have been observed to be between six months to six years on average.
One area of debate is the distance of the star. Using the most recent and modern direct parallax measurements resulted in a distance of 495 light years. However, using the star's natural radio emissions for parallax yields a distance of 640 light years. Allowing for the high amount of infrared radiation emitted from the star and the absorption of light by its circumstellar dust disk, a compromise distance of 570 light years is most often used.
At the compromise distance of 570 light years, the star has a total bolometric luminosity some 85,000 times that of the Sun. Because Betelgeuse is so immense in size, it is easy to measure its angular diameter, which is 0.054 seconds of arc. This places the radius of the star at some 3.6 AU, or as great as that of the asteroid belt (with a total diameter of 7.2 AU). Measuring the star in ultraviolet light has suggested its radius is over 8 AU in size, more than twice the distance found at optical wavelengths.
Due to its extremely high mass though, the star is fusing core helium into carbon and oxygen, which has swelled the outer layers of gas in the star, causing its great size. Eventually the star will fuse heavier elements all the way to iron before collapsing into a supernova. Such an explosion would be so bright, it would outshine the full moon. A date for the nova has been set by some at 2012; others however are more skeptical, as astronomers have claimed such a prediction is impossible to tell.
The UC Berkeley's Infrared Spatial Interferometer (ISI) atop Mt. Wilson Observatory in Southern California collected evidence over 15 consecutive years, showing the star is constantly contracting. The star is estimated to have shrunk 15 percent in size since 1993 and the rate of contraction is increasing, the total observed contraction is equal to half an astronomical unit, or equivalent of the distance of Venus from the sun. It is speculated this is the behavior expected for a star that has reached the end of its life and the beginning of gravitational collapse. Because of the mass of Betelgeuse, the result of the supernova explosion will be either a neutron star or even a black hole.
Updated high resolution images of Betelgeuse obtained by the Very Large Telescope in Chile in July 2009, revealed new evidence that Betelgeuse is rapidly shedding mass. A large gas plume is shown to be surrounding the star. If the plume was in our solar system, it would extend to the orbit of Jupiter. The plume is viewed as further evidence by scientists the star is very near the end of its life.