Castor (star)

Castor

The position of Castor within the Gemini Constellation.
Observation data Epoch J2000      Equinox J2000
Constellation	Gemini
Right ascension	07h 34m 36s
Declination	+31° 53' 18"
Apparent magnitude (V)	1.96 / 2.91
Characteristics
Spectral type	A1 V / A2 Vm
U−B color index	0.02
B−V color index	0.04
Astrometry
Radial velocity (Rv)	5.2 / −1.2 km/s
Proper motion (μ)	RA: −206.33 mas/yr Dec.: −148.18 mas/yr
Parallax (π)	65.50 ± 1.10 mas
Distance	49.8 ± 0.8 ly (15.3 ± 0.3 pc)
Absolute magnitude (MV)	1.33 /2.28
Details
Mass	2.15 / 1.7 M☉
Radius	2.3 / 1.6 R☉
Luminosity	30 / 14 L☉
Temperature	10,300 / 8,840 K
Metallicity	950% / 280% Sun
Age	200 million years
Other designations
Castor, α Gem, 66 Gem, YY Gem, Gl 278, HR 2891, BD +32 1581/2, HD 60178/60179, GCTP 1785.00, LTT 12038, SAO 60198, FK5 287, ADS 6175, Struve 1110, HIP 36850.
Database references
SIMBAD	Castor Aa data
Database references
SIMBAD	Castor Ba data

Castor (α Gem, α Geminorum, Alpha Geminorum) is the second brightest star in the constellation Gemini and one of the brightest stars in the night sky. Although it has the Bayer designation "alpha", it is actually fainter than Beta Geminorum (Pollux). Castor is 49.8 light years away from Earth.

Physical characteristics

Castor was discovered to be a visual binary in 1678, with the magnitude of its components being 2.0 and 2.9 (the combined magnitude is 1.58). The separation of the components is about 6" and the period of revolution is around 467 years. Each of the components of Castor is itself a spectroscopic binary, making Castor a quadruple star system. Castor has a faint companion separated from it by about 72" but having the same parallax and proper motion; this companion is an eclipsing binary system with a period slightly less than 1 day, and it is one of only a few known eclipsing binary systems where both companions are class M dwarf stars. Castor can thus be considered to be a sextuple star system, with six individual stars gravitationally bound together. Component C has the variable star designation YY Geminorum.

The Castor system

Parameter	Star Component
	Aa	Ab	Ba	Bb	Ca	Cb
Spectral type	A1 V	Unknown (probably M5 V)	A2 Vm	M2 V	M0.5 Ve	M0.5 Ve
Mass (M☉)	2.15	0.4–0.6	1.7	0.4–0.6	0.62	0.57
Radius (R☉)	2.3	?	1.6	?	0.76	0.68

Etymology and culture

Castor and Pollux are the two "heavenly twin" stars that give the constellation Gemini (meaning twins in Latin) its name. The name Castor refers specifically to Castor, one of the twin sons of Zeus and Leda, and literally means beaver in the Greek. The star was annotated by the Arabic description Al-Ras al-Taum al-Muqadim, which translates as the head of the foremost twin. In the catalogue of stars in the Calendarium of Al Achsasi Al Mouakket, this star was designated Aoul al Dzira, which was translated into Latin as Prima Brachii, meaning the first in the paw.

In Chinese, 北河 (Běi Hé), meaning North River, refers to an asterism consisting of Castor, ρ Geminorum and Pollux. Consequently, Castor itself is known as 北河二 (Běi Hé èr, English: the Second Star of North River.) The Chinese recognized Castor as Yin, which is, according to the Chinese, one of the two fundamental principles upon which all things depend.^{[citation needed]}

Castor as the name

USS Castor (1869) and USS Castor (AKS-1), both of United States navy ships.

External links

• "Castor 6". SolStation. http://www.solstation.com/stars2/castor6.htm. Retrieved December 5, 2005.