Bellatrix, also known by its Bayer designation Gamma Orionis (γ Ori, γ Orionis), is the third brightest star in the constellation Orion. A second-magnitude star, it is the twenty-seventh brightest star in the night sky. The name Bellatrix is Latin for female warrior. In the Alfonsine tables, it was also called the Amazon Star, a loose translation of the Arabic name Al Najīd, the Conqueror. It forms the left shoulder of Orion the Hunter.[11] Bellatrix is one of the four navigational stars in Orion that are used for celestial navigation.[12] The Chinese name for the star is 参宿五 ("The Fifth of the Three Stars").

This is a massive star with about 8.4 times the Sun's mass. It has an estimated age of approximately 20 million years;[5] long enough for a star of this mass to consume the hydrogen at its core and begin to evolve away from the main sequence into a giant star.[7] The effective temperature of the outer envelope of this star is 22,000 K,[8] which is considerably hotter than the 5,778 K on the Sun. This high temperature gives this star the blue-white hue that occurs with B-type stars.[13] The measured angular diameter of this star, after correction for limb darkening, is 0.72 ± 0.04 mas.[14] At an estimated distance of 250 light-years (77 parsecs),[1] this yields a physical size of about six times the radius of the Sun.[6][7]

Since 1963, Gamma Orionis was included with a set of bright stars that astronomers employ as a luminosity standard. These are used for comparison with other stars to check for variability, and so by definition, the apparent magnitude of Gamma Orionis was set to 1.64. However, when an all-sky photometry survey was carried out in 1988, this star was itself found to be variable. It ranges in apparent magnitude from 1.59 to 1.64.[15]

Bellatrix was once thought to belong to the Orion OB1 Association of stars that share a common motion through space, along with the "Orion's Belt" stars ζ Ori (Alnitak), ε Ori (Alnilam), and δ Ori (Mintaka). However, this is no longer believed to be the case, as Gamma Orionis is now known to be much closer than the rest of the group.[7] It is not known to have a stellar companion.[16] A 2011 search for nearby companions failed to conclusively find any objects that share a proper motion with Bellatrix. Three nearby candidates were all found to be background stars.[5]

Excerpt from Wikipedia.