Orion's Belt
Orion's Belt is an asterism in the constellation of Orion. Other names include the Belt of Orion, the Three Kings, and the Three Sisters. The belt consists of three bright and easily identifiable collinear star systems – Alnitak, Alnilam, and Mintaka – nearly equally spaced in a line, spanning an angular size of ~.
Owing to the high surface temperatures of their constituent stars, the intense light emitted is blue-white in color. In spite of their spot-like appearance, only Alnilam is a single star; Alnitak is a triple star system, and Mintaka a sextuple. All three owe their luminosity to the presence of one or more blue supergiants. The brightest as viewed from the Sun is Alnilam, with an apparent magnitude of 1.69, followed by Alnitak at 1.74 and Mintaka at 2.25. The ten stars of the three systems have a combined luminosity approximately a million times that of the Sun.
Orion's Belt appears widely in historical literature and in various cultures, under many different names. It has played a central role in astral navigation in the Northern hemisphere since prehistoric times. It is considered to be among the clearest constellations in the winter sky, although it is not visible during summer, when the Sun is too visually close.Belt features
The names of the three stars that comprise the belt derive from Arabic. All three were once known as Al Niṭhām meaning "string of pearls" with spelling variants that include Alnihan and Ainilam, which was suggested by Knobel to be mistakes in transliteration or copy errors.Alnitak
Alnitak is a triple star system at the eastern end of Orion's belt and is 1,260 light-years from the Earth. Alnitak B is a 4th-magnitude B-type star which orbits Alnitak A every 1,500 years. The primary is itself a close binary, comprising Alnitak Aa and Alnitak Ab. Alnitak Aa is estimated to be up to 28 times as massive as the Sun and have a diameter 20 times greater. It is the brightest star of class O in the night sky.Alnilam
Alnilam is a singular B0 supergiant, approximately 2,000 light-years away from Earth and magnitude 1.69. It is the 29th-brightest star in the sky and the fourth-brightest in Orion. It is 375,000 times more luminous than the Sun. Its spectrum serves as one of the stable anchor points by which other stars are classified.Mintaka
Mintaka is a six-star system at the western end of the Belt, and the star system closest to the celestial equator. It is the nearest massive multiple stellar system, composed of three spectroscopic components. The most luminous individual star is a O9.5 II blue giant. Together, the system has a combined ~250,000 solar luminosity. Mintaka is 1,200 light-years distant, with a visual magnitude of 2.25. The innermost binary has a period of 5.732 days and a semi-major axis of approximately 32 million kilometers, with the two massive stars eclipsing each other twice per completed orbit as viewed from Sol, from which regular minor dips in brightness arise.