Castor (star)
Castor (Latin spelling, literally means " beaver ") or ( Greek) Castor is the second brightest star in the constellation Gemini. Although somewhat fainter than its neighbor star Pollux in the same constellation, he wears in astronomy Bayersche the designation α Geminorum.
He has long been considered double star known, but in fact a rarely occurring system of 6 stars. It can be separated into 2 or 3 stars only in the telescope; freiäugig it appears as a white single star first size (1.5 mag), while the slightly more Pollux ( β Geminorum ) reddish irradiated with 1.2 and like to act around a quarter lighter.
The names " Castor and Pollux " stand for the offset of Zeus at the starry sky of the Dioscuri twins, where Castor was mortal of Greek mythology, the half-brothers.
In ancient records and in astrology the stars Castor and Pollux were always regarded as belonging together. Highlight the constellation of the heads of the two inseparable twins. The two stars together form a corner of the so-called Wintersechsecks.
A 6- fold star system
That Castor, which is about 51 light-years away from us, represents a complex multiple star system, only in recent decades is well known. The six stars are grouped in three pairs of stars that revolve around each other tightly as they orbit their common center of gravity, the barycenter, on highly elliptical orbits.
The three pairs of stars are themselves spectroscopic binaries, ie, which can also be the largest telescope not separate, but differing only on the basis of periodic changes in their spectrum. On two of the binaries ( ie 4 of the 6 suns ) account for about 99.8 percent of the total radiation.
Referred to these two main components, briefly as α A and α Gem Gem B, are 1.9 and 2.9 may like bright and include the spectral types A1 and A2m on. Their orbital period is 420 years. Both are spectroscopic, not optically resolvable binaries that belong to luminosity class V. Accordingly, any 4 suns (as well as our day-star ) so-called main sequence stars.
The third component, just as α Gem C, with the alternative designation YY Geminorum is an eclipsing variable star, consisting of two red dwarfs. YY Geminorum is only 8.07 likes bright and encircles the Castor system at a distance of about 70 " of the components A and B. The position angle of 164 ° to A.
The three main stars can be observed with the telescope, the separation of the standing closer together A and B from year to year will be easier, as they strive currently seen from the Earth apart. At present ( 2011) is needed to resolve a telescope with about 5 centimeters lens aperture required.
Change of position angle and angular spacing of the two main components A and B Castor: