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. Together with Delta Orionis (Mintaka) and Epsilon Orionis (Alnilam), the three stars make up the belt of Orion, known by many names across many ancient cultures. Zeta Orionis (ζ Ori) is the left-most star.

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.

Observation history

Alnitak has been known since antiquity and, as a component of Orion's belt, has been of widespread cultural significance. It was discovered to be a double star by amateur German astronomer George K. Kunowsky in 1819. The bright primary was found to have a close companion in 1998 by a team from the Lowell Observatory after being suspected in the 1970s from observations 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.

System

Alnitak is a triple star system at the eastern end of Orion's belt lying approximately 800 light years from the Solar System. The primary, now known as Alnitak Aa as it itself is a close binary, is a blue supergiant of spectral and luminosity type O9.7 Ibe, with an absolute magnitude of -5.25. It is estimated as being up to 28 times as massive as the sun, and having 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 1500 years. The third star, Alnitak Ab, was only discovered in 1998. It is a 4th magnitude O-type star.

The Alnitak system is bathed in the nebulosity of IC 434.

Etymology and cultural significance

The traditional name Alnitak, alternately spelled Al Nitak or Alnitah, the name is taken from the Arabic النطاق an-nitaq, "the girdle".

Orion's belt

The three belt stars were collectively known by many names in many cultures. Arabic terms include النجاد Al Nijād 'the Belt', النسك Al Nasak 'the Line', العلقات Al Alkāt 'the Golden Grains or Nuts' and, in modern Arabic, ميزان الحق Al Mīzān al H•akk 'the Accurate Scale Beam'. In Chinese mythology they were also known as The Weighing Beam. The belt was also the Three Stars mansion one of the Twenty-eight mansions of the Chinese constellations. It is one of the western mansions of the White Tiger.

In pre-Christian Scandinavia, the belt was known as Frigg's Distaff (Friggerock) or Freyja's distaff. Similarly Jacob's Staff and Peter's Staff were European biblical derived terms, as were the Three Magi, or the Three Kings. Väinämöinen's Scythe (Kalevala) and Kalevan Sword are terms from Finnish mythology.

The Seri people of northwestern Mexico call the three belt stars Hapj (a name denoting a hunter) which consists of three stars: Hap (mule deer), Haamoja (pronghorn), and Mojet (bighorn sheep). Hap is in the middle and has been shot by the hunter; its blood has dripped onto Tiburón Island.

See also

• Zeta Orionis in fiction

References

External links

• .