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Alnitak or Zeta Orionis is a triple star system at the eastern end of Orion's belt. It is a 1.79 apparent magnitude blue supergiant, 30 000 times more luminous than the Sun. Its primary's absolute magnitude is -6.6. The name is taken from the Arabic an-nitaq, “the belt”. It has at least two companion stars of magnitudes 4.0 and 10.2. The magnitude 1.9 and 4.0 stars are separated by 2.3 arcseconds. The Alnitak system is bathed in the nebulosity of IC 434. A triple star system consists of three gravitationally bound stars. ... Orion, a constellation often referred to as The Hunter, is a prominent constellation, perhaps the best-known in the sky. ... The apparent magnitude (m) of a star, planet or other heavenly body is a measure of its apparent brightness; that is, the amount of light received from the object. ... A supergiant is a very large type of star which is ~10 to 50 solar masses on the Hertzsprung-Russell diagram. ... In astronomy, absolute magnitude is the apparent magnitude, m, an object would have if it were at a standardized distance away. ... A second of arc or arcsecond is a unit of angular measurement which comprises one-sixtieth of an arcminute, or 1/3600 of a degree of arc or 1/1296000 ≈ 7. ... IC 434, the Horsehead Nebula. ...
Like all O stars, Alnitak is a source of X-rays that seem to come from a stellar wind that blows from its surface at nearly 2,000 km/s; the X-rays are produced when blobs of gas in the wind crash violently into one another.
Alnitak is probably only about 6 million years old and will eventually become a red supergiant before exploding as a supernova.
Alnitak is the easternmost of the three stars of Orion's Belt, with Alnilam in the center and Mintaka in the west.
Alnitak lies in a region crowded with several dusty clouds of interstellar gas actively forming new stars, including the famous "Horsehead Nebula" to the south.
Alnitak Aa is a blue supergiant star of spectral and luminosity type O9.7 Ibe (with "peculiar" emission lines), where O-type stars are the hottest stars in the spectral sequence excluding white dwarfs.
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