Alnitak is pronounced ALL-nit-ahk. Alnitak (Zeta Orionis, 50 Ori) is a triple star system at the eastern end of Orion's belt, and is 736 light years from the Earth. It has 100,000 times the luminosity of the sun. The primary (Alnitak A) is itself a close binary, comprising Alnitak Aa (a blue supergiant of spectral and luminosity type O9.7 Ibe, with an absolute magnitude of -5.25 and an apparent magnitude of 2.0) and Alnitak Ab (a blue dwarf of spectral and luminosity type O9V, with an absolute magnitude of about -3.0 and an apparent magnitude of about 4, discovered in 1998 ). Aa is estimated as being up to 28 times as massive as the sun, and to have a diameter 20 times greater. It is the brightest star of class O in the night sky. Alnitak B is a 4th magnitude B-type star which orbits Alnitak A every 1500 years. A fourth star, 9th magnitude Alnitak C, has not been confirmed to be part of the Aa-Ab-B group, and may simply lie along the line of sight.
The Alnitak system is bathed in the nebulosity of IC 434. Source: Wikipedia -