Alnitak

Alnitak (also Al Nitak ) is the name for the star ζ Orionis (Zeta Orionis ), the easternmost belt star in Orion. The name (Arabic النطاق to - niṭāq ) means " belt". Alnitak is a multiple star, and has an apparent magnitude of 2.03 mag.

The main star Alnitak Aa belongs to the spectral class O9, its surface temperature is about 25,000 Kelvin. As Beta, Delta and Epsilon Orionis is Zeta Orionis a luminous blue supergiant with 100,000 times the bolometric luminosity of our sun. In the visual area its luminosity is about 10,000 times greater than that of the sun. Alnitak has about 20 times the diameter of our sun. The distance from Alnitak is approximately 800 light years. Alnitak Aa has a close companion named Alnitak Ab, which was discovered only in 2000. It is in this star probably around a main sequence star of spectral type O with about 23 times the sun's mass. The apparent brightness is about 4 mag and the luminosity in the visual area amounts corresponding to about 1,300 times the solar luminosity. In an angular distance of 2.3 " at a position angle of 165 degrees, there is a slight observable companion Alnitak B. His brightness is like 4.2 at about 1,100 times the visual solar luminosity, the spectral type B0 III, the mass is at about 13 solar masses estimated. In the immediate vicinity of the Horsehead Nebula and Flame Nebula as parts of the Orion Nebula complex.

Belt of Orion: Alnitak is the bright star at the bottom left