Rigel, << RY jehl, >> also known as Beta Orionis, ranks as the eighth brightest star in Earth’s sky. Only the sun and six other stars appear brighter. Rigel also ranks as the brightest star in Orion, the Hunter, forming the constellation’s western foot. The name Rigel comes from Arabic words meaning foot of the giant. Rigel far outshines any other star in our region of the galaxy, giving off about 40,000 times as much light as does the sun. Other stars appear brighter than Rigel only because Rigel is relatively far from Earth. It lies between 700 and 900 light-years away. One light-year is the distance light travels in a vacuum in a year, about 9.46 trillion kilometers (see Light-year ).
Rigel contains about 17 times the sun’s mass (amount of matter). Its diameter measures about 70 times that of the sun. Because massive stars burn out quickly, astronomers know that Rigel can be no more than a few million years old. Rigel’s bluish-white color results from its relatively high surface temperatures, around 11,000 K. One kelvin (K) equals one Celsius degree above absolute zero (–273.15 °C). Some astronomers consider Rigel an outlying member of a group of relatively young stars called the Orion OB1 association. The association includes other stars in the constellation’s belt and sword.
Astronomers classify Rigel as an extremely large, hot type of star called a B supergiant. A B supergiant has burned up all the hydrogen in its core and is rapidly developing toward a stellar explosion called a supernova. Rigel will exhaust its nuclear fuel and explode as a supernova within 10 million years.
Rigel is actually the largest member of a triple star system. Its two companion stars, Rigel B and Rigel C, have a similar temperature to the larger star, Rigel A, but about 1/10 of its mass and radius. Rigel B and Rigel C orbit each other at about the same distance that Neptune orbits the sun. Together, the two stars orbit Rigel A at roughly 70 times this distance.
Rigel A has the spectral type B8Ia. Rigel B and C have the type B9V. For more information on spectral classification, see Star (The Hertzsprung-Russell diagram) .
See also Orion ; Star (table: The 10 brightest stars as seen from Earth) .
