Friday, April 22, 2011

Zeta Orionis

Zeta Orionis (ζ Ori), traditionally known as Alnitak (Arabic: النطاق an-niṭāq‎), is a triple star some 800 light years distant in the constellation Orion. It is part of Orion's Belt along with Delta Orionis (Mintaka) and Epsilon Orionis (Alnilam).
The primary star is a hot blue supergiant with an absolute magnitude of -5.25, and is the brightest class O star in the night sky with a visual magnitude of 1.70. It has two bluish 4th magnitude companions. The stars are members of the Orion OB1 association and the Collinder 70 association.
Much more recently, in 1998, the bright primary was found by a team from the Lowell Observatory to have a close companion; this had been suspected from observations made with the Narrabri Stellar Intensity Interferometer in the 1970s. Initially thought to be around 1500 light years distant, the Alnitak system was found to be almost twice as close following measurement of its stellar parallax by the Hipparcos satellite published in 1996. Alnitak has a magnitude of +2.04.

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