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Rigel (β Ori, β Orionis, Beta Orionis) is the brightest star in the constellation Orion and the sixth brightest star in the sky, with visual magnitude 0.18. Although it has the Bayer designation "beta", it is almost always brighter than Alpha Orionis (Betelgeuse).


Physical properties

Rigel is well beyond the current range of accurate parallax measurements: spectroscopic estimates place its distance between 700 and 900 light-years (210 and 280 pc), while Hipparcos's “best guess” is 773 light-years (237 pc), with a margin of error of about 19%.[4] It is a blue supergiant, at 17 solar masses, shining with approximately 85,000 times the luminosity of the Sun.[5] Rigel is the most luminous star in our local region of the Milky Way; the nearest more powerful star is Naos, almost 1,100 light years away in Puppis. The star is so bright that when at 1 astronomical unit from the star, it shines as an extremely bright ball with an angular diameter of 35° with magnitude -38. The power flux is 100 MW / m2 or 10kW / cm2, compared to the Sun's flux of 1.4kW / m2. The power flux at this distance is the same as the flux a few millimeters from a welding arc; any object this close will be vaporized and blown away by the strong stellar wind.

As it is so bright and it is moving through a region of nebulosity, Rigel lights up several dust clouds in its general vicinity, the most notable being the IC 2118 (the Witch Head Nebula).[6] Rigel is also associated with the Orion Nebula, which—while more or less along the same line of sight as the star—is almost 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 specifically, it is a member of the Taurus-Orion R1 Association, with the OB1 Association reserved for stars closer to the nebula and more recently formed.[6]

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