Re: Analisi di tipo astronomico-astronautico
Inviato da ivan il 13/3/2006 21:12:51
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.
Written by Jim Kaler.
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