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RIGEL (Beta Orionis). Like its rival in Orion, Betelgeuse, Rigel (Beta Orionis) is a supergiant. Its name comes from the same root as Betelgeuse's, originally "rijl Al-jauza," meaning the "foot" of al-jauza, the Arabs "Central One." For us, the star represents the left foot of Orion, the mythical hunter. It is usually pictured as perched upon a fainter star, Cursa (Beta Eridani), which represents the hunter's foot stool. Though Rigel is Orion's Beta star, it appears to us somewhat brighter than the Alpha star, Betelgeuse, perhaps suggesting that Betelgeuse was somewhat brighter in times past. Rigel ranks 7th in visual brightness, just behind Auriga's Capella. At a distance of 775 light years, Rigel actually shines with the light of 40,000 Suns. It is a "blue supergiant," a fairly hot star with a surface temperature (11,000 Kelvin) about double that of our Sun. Its warmer temperature gives it a bluish-white light that contrasts beautifully with Betelgeuse. If the hot star's invisible ultraviolet radiation is considered, the luminosity climbs to 66,000 solar, the radiation pouring from a star 70 times the solar size. Rigel is accompanied by a fairly bright, seventh magnitude companion nine seconds of arc away. Normally such a star is easily found in a small telescope, but Rigel's brilliance nearly overwhelms it. The companion, at least 50 times farther from Rigel than Pluto is from the Sun, is itself double, the components much fainter and much less massive class B main sequence stars that are fusing hydrogen into helium. With an original mass around 17 times that of the Sun, Rigel is in the process of dying, and is most likely fusing internal helium into carbon and oxygen. The star seems fated to explode, though it might just make it under the wire as a rare heavy oxygen-neon white dwarf. Rigel is a part of a large association whose stars are related by birth. The group includes the stars of Orion's Belt, the Orion Nebula of Orion's sword and its illuminating stars, and many of the other hot blue-white stars in the constellation.
Rigel, Beta Orionis, is the seventh brightest star in the sky at magnitude 0.18. Though designated "Beta" for Orion, it actually appears brighter than the "Alpha", Betelgeuse. The distance to Rigel is somewhere between 700 and 900 light years; Hipparcos' best guess is 773 light years (237 parsecs), but that far out the range of error is quite large. Rigel is a B8 Ia supergiant, and shines with approximately 40,000 times the brightness of the sun. It is far and away the most luminous star in the local region of space Milky Way; the nearest more powerful star is Deneb, as much as 3300 light years (1000 parsecs) down the Orion Arm. As it is so bright, and is moving through a region of nebulosity, it should come as no surprise to learn that Rigel lights up several dust clouds in its general vicinity. The most notable is the Witch Head Nebula. Rigel is also associated with the Orion Nebula, which -- while along the more or less the same line of sight as the star -- is about twice as far away from Earth. Despite the difference in distance, projecting Rigel's path through space for its expected age brings it close to the nebula. As a result, Rigel is sometimes classified as an outlying member of the Orion OB1 Association , along with many of the other bright stars in that region of the sky; more commonly it is considered a member of the Taurus-Orion R1 Association , and the OB1 association is reserved for stars closer to the nebula and more recently formed. Rigel is believed to be a triple star. The main star is orbited by two smaller companions, Rigel B and C, which orbit one another closely at 28 AU and in turn orbit around Rigel as a unit, at a distance of about 2000 AU. It is also variable, in the slight, irregular way common to supergiants. The range of variability is from 0.03 to 0.3 of a magnitude, about three to thirty percent, over an average of 25 days. A fourth star in the system is sometimes proposed, but it is generally considered that this is a misinterpretation of the main star's variability, which may be caused by physical pulsation of the surface. The star's name comes from its location at the "left foot" of Orion. It is a contraction of "Rijl Jauza al-Yusra", this being Arabic for "left foot of the Central One".