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).

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Betelgeuse is a vertex of the Winter Triangle.

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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 http://iapetus.phy.umist.ac.uk/rdor/rdor.html, 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.

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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.

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Alpha: The first letter of the Greek alphabet, Α α, also has some cultural meanings; see alpha (letter)....

Constellation: A constellation is a group of stars visibly related to each other in a particular configuration. In three-dimensional space, most of the stars we see have little relation to one another, but can appear to be grouped on the celestial sphere of the night sky. Humans excel at finding patterns and throu...

Orion: Orion is a proper name used in many different ways:...