Belt of Orion

Orion's Belt or the Belt of Orion, also known as the Three Kings or Three Sisters, is an asterism in the constellation Orion. It consists of the three bright stars Alnitak, Alnilam and Mintaka.

Looking for Orion's Belt in the night sky is the easiest way to locate Orion in the sky. The stars are more or less evenly spaced in a straight line, and so can be visualized as the belt of the hunter's clothing. They are best visible in the early night sky during the Northern Winter/Southern Summer, in particular the month of January at around 9:00 pm.

The names of the three stars come from Arabic; Alnilam comes from النظام which means "string of pearls"; Mintaka (منطقة) has the same root as Alnitak (النطاق) and both mean "belt".

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 817 light-years from the Earth. It has 100,000 times the luminosity of the Sun. Considering ultraviolet light, its luminosity comes out at 250,000 times that 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 1,500 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.

Alnilam (Epsilon Orionis, 46 Ori) is approximately 1,340 light-years away from Earth and shines with magnitude 1.70. Considering ultraviolet light Alnilam is 375,000 times more luminous than the Sun. It is a large blue supergiant star in the constellation of Orion. Its Flamsteed designation is 46 Orionis.

It is the 29th-brightest star in the sky and the fourth-brightest in Orion.

...
Wikipedia