Rigel

Rigel (Orionis / Beta Orionis) is the brightest star in the constellation Orion and the seventh brightest star in the sky, with visual magnitude 0.18.

Although it has the Bayer designation "beta", it is actually brighter than Alpha Orionis (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".

Another Arabic name is "the foot of the great one" (giant, conqueror, etc.), which is also the source of the variant name Algebar.

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