Alnitak

Alnitak[edit]

Alnitak, also designated ζ Orionis and 50 Orionis, is a triple star system in the constellation of Orion. It is one of the three main stars of Orion's Belt along with Alnilam and Mintaka. The primary star, Alnitak Aa, is a hot blue supergiant with an absolute magnitude of -6.0 and is the brightest class O star in the night sky with a visual magnitude of +2.0. It has two bluish 4th magnitude companions, producing a combined magnitude for the trio of +1.77.

Observational history[edit]

Alnitak has been known since antiquity and is of widespread cultural significance as part of Orion's Belt. The bright primary was found to have a close companion in 1998 by a team from the Lowell Observatory, which had been suspected from observations made with the Narrabri Stellar Intensity Interferometer in the 1970s.

Stellar system[edit]

Alnitak is a triple star system at the eastern end of Orion's Belt, with a 4th magnitude companion nearly 3 arc-seconds distant, in an orbit taking over 1,500 years. Alnitak Aa is a blue supergiant of spectral type O9.5Iab and is estimated to be up to 33 times as massive as the Sun and 20 times larger in diameter. It is about 21,000 times brighter than the Sun. Alnitak Ab is a blue subgiant of spectral type B1IV with an apparent magnitude of 4.3, discovered in 1998.

Etymology and cultural significance[edit]

The traditional name Alnitak is derived from the Arabic النطاق an-niṭāq, "the girdle". In 2016, the IAU organized a Working Group on Star Names (WGSN) to standardize proper names for stars. The WGSN approved the name Alnitak for the star ζ Orionis Aa.

Orion's Belt[edit]

The three belt stars were known by many names in various cultures, including النجاد Al Nijād 'the Belt' and النسك Al Nasak 'the Line' in Arabic, and The Weighing Beam in Chinese mythology. In Chinese astronomy, 參宿 (Shēn Xiù), meaning 'Three Stars (asterism)', refers to an asterism consisting of Alnitak, Alnilam, and Mintaka.

Namesakes[edit]

The USS Alnitah was a United States Navy Crater-class cargo ship named after the star.

References[edit]

External links[edit]

"Alnitak 3". SolStation. Retrieved 2005-12-15.
NASA Astronomy Picture of the Day: Image of Alnitak (12 January 2010)

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