Orion's Belt
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.[1]
Component stars
Alnitak
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 [2]). Aa is estimated as being up to 28 times as massive as the sun, and to have a diameter 20 times greater.[3] 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.
Alnilam
Alnilam (Epsilon Orionis, 46 Ori) is approximately 1340 light years away from earth and shines with magnitude 1.70. Considering ultraviolet light Alnilam is 375,000 times more luminous than the Sun.[2] 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 (the 4th brightest in Orion) and is a blue-white supergiant. Together with Mintaka and Alnitak, the three stars make up the belt of Orion, known by many names across many ancient cultures. Alnilam is the middle star.
Since 1943, the spectrum of this star has served as one of the stable anchor points by which other stars are classified.[1] It is also one of the 57 stars used in celestial navigation. It is at its highest point in the sky around midnight on December 15.
Alnilam's relatively simple spectrum has made it useful for studying the interstellar medium. Within the next million years, this star may turn into a red supergiant and explode as a supernova. It is surrounded by a molecular cloud, NGC 1990, which it brightens to make a reflection nebula. Its stellar winds may reach up to 2000 km/s, causing it to lose mass about 20 million times more rapidly than the Sun.
Mintaka
Mintaka (Delta Orionis, 34 Ori) is 915 light years away and shines with magnitude 2.21. Mintaka is 90,000 times more luminous than the Sun. Mintaka is a double star. The two stars orbit around each other every 5.73 days.[3]
References in history and culture
The same three stars are known in Spain, Portugal and South America as Las Tres Marías. They also mark the northern night sky when the sun is at its lowest point, and were a clear marker for ancient timekeeping. In the Philippines and Puerto Rico they are called the Los Tres Reyes Magos.[5] The stars start appearing around the holiday of Epiphany, when the Biblical Magi visited the baby Jesus, which falls on January 6.
Richard Hinckley Allen lists many folk names for the Belt of Orion. The English ones include: Jacob's Rod or Staff; Peter's Staff; the Golden Yard-arm; the L, or Ell; the Ell and Yard; the Yard-stick, and the Yard-wand; the Ellwand; Our Lady's Wand; the Magi; the Three Kings; the Three Marys; or simply the Three Stars.[6]
The passage "Canst thou bind the sweet influences of Pleiades, or loose the bands of Orion?" is found in the Bible's Book of Job[7] and Book of Amos.[8]
In Finnish mythology, the Orion's belt is called Väinämöisen vyö (Väinämöinen's belt). The stars which appear to "hang" off the belt form an asterism called Kalevanmiekka (Kaleva's sword).
Tennyson's poem The Princess describes Orion's belt as:
..those three stars of the airy Giant's zone,
That glitter burnished by the frosty dark.[9]
In Arabic, Alnilam means "string of pearls". Mintaka means "belt" and comes from the word alnitak النطاق an-niṭāq which means "the belt".
Gallery
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Map of Orion. -
CGI of Orion's Belt. -
Astrophotograph of the region of Alnitak (upper right) and the Flame Nebula.
See also
References
- ^ Dolan, Chris. "Orion". Archived from the original on 2011-11-28. Retrieved 2011-11-28.
- ^ "Alnilam". Jim Kaler's Stars. University of Illinois, Urbana-Champaign Campus. 2009. Archived from the original on 2011-11-28. Retrieved 2011-11-28.
- ^ "Mintaka". Jim Kaler's Stars. University of Illinois, Urbana-Champaign Campus. 2009. Archived from the original on 2011-11-28. Retrieved 2011-11-28.
- ^ "Orion Watching Over ALMA". ESO Picture of the Week. Retrieved 20 August 2012.
- ^ http://sepiensa.org.mx/contenidos/s_reyes/reyes.htm
- ^ Allen, Richard Hinkley. "Star Names — Their Lore and Meaning".
- ^ Job 38:31
- ^ Amos 5:8
- ^ Alfred Lord Tennyson's poem: The Princess