mardi 8 juillet 2008

Capricornus 11

Considering its importance, Capricornus is rather faint; the asterism of a horned animal isn't terribly evident, and the Bayer stars are generally third to fourth magnitude.
Alpha Capricorni is known as Al Giedi or Algedi (the goat or ibex).
This is a double star, alpha1 and alpha2 Capricorni. Alpha2 is the primary, although they only make an optical pair. Each star is however a visual binary (see below for details).

Beta Capricorni is called Dabih, from the Arabic Al Sa'd al Dhabih meaning "The Lucky One of the Slaughterers". This name indicates that the star served to signal the beginning of a winter ritual, possibly the very ones depicted on the pottery examples shown above. For the sun would have been in this constellation at the winter solstice three to four thousand years ago; were they beseeching the gods to bring back the Spring?

Delta Capricorni is the brightest star of the constellation (as well as an eclipsing binary). The Arabs called delta and nearby gamma Capricorni "The Two Friends".

Double stars in Capricornus:Alpha2 and alpha1Cap form an optical binary of yellow and orange stars: 3.6, 4.2; PA 291º, separation 378". Each star is a visual binary:
Alpha1 Capricorni: 4.6, 9.2; 221º, 45.4".Alpha2 Capricorni: 3.5, 9.5; 156º, 154".
Beta Capricorni is a wide visual binary with a nice colour contast, yellow and blue: 3.1, 6; PA 267º, separation 205".

Tau Capricorni is a visual binary with a 95 year orbit: 5.5, 7; PA 107º, separation 0.4".

The PA is increasing, the separation is decreasing; at the year 2000 the values will be 123º and 0.2".

Variable stars in Capricornus:
The only variable worth noting is delta Capricorni, which is an eclipsing binary (2.81-3.05) with a period of 24h32m47.2s.

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