|Designation|| ζ Sco|
|Right ascension||16h 53m 59.7270s|
|Declination||-42° 21′ 43.3137″|
|Type of object||Hypergiant star|
|Magnitude|| Apparent Mag: 4.705|
Absolute Mag: -8.5
|Distance from Earth||2,600 ly|
|Radial velocity||-26.00±0.8 km/s|
|Proper motion|| RA: 0.009 mas/yr|
Dec.: -2.939 mas/yr
Zeta Scorpii (ζ Sco, ζ Scorpii, HD 152236) is a Bayer designation shared by two stars in the constellation of Scorpius.Zeta-1 Scorpii is a hypergiant star whereas Zeta-2 Scorpii is a giant star. Although these stars appear only 7 arcminutes apart in the night sky, they only form a visual binary, meaning they only appear to be close to one another as they lie along the same line of sight. In fact, Zeta-1 Scorpii is 40 times further away than Zeta-2 Scorpii. The star Zeta-1 Scorpii is one of the most luminous stars known, thought to be nearly a million times brighter than the Sun. This article discusses Zeta-1 Scorpii unless explicitly said.
Properties and Structure
Zeta-1 Scorpii (sometimes written as ζ1 Scorpii) is a B type hypergiant star and part of the open cluster NGC 6231. It is also a candidate luminous blue variable star. The star's surface is incredibly hot with a temperature of 21,000 kelvin. Unsurprisingly for a hypergiant star, it it truly massive; it is thought to have a mass of 36 solar masses though some sources place it at 60) and radius 103 times that of the Sun. This large temperature and size means the star's luminosity is 850,000 times that of the Sun. Large dust clouds situated in between Zeta-1 Scorpii and Earth attenuate its great luminosity so it only appears as a fourth magnitude star. These are also thought to change the color to be a dull yellow.
Zeta-2 Scorpii is a K type giant star lying closer than Zeta-1 Scorpii at only 151 light years. It is smaller than Zeta-1 Scorpii but is brighter with a magnitude that varies between 3.59 and 3.65. This corresponds to an absolute magnitude of around 0.3. It is smaller with a mass of 1.19 solar masses and a radius 21 times larger than the Sun.
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