Capricornus

Capricornus

Transit Date of principal star:
26 July

Capricornus (or Capricorn) is usually translated as "The Sea Goat" or "The Goat-Fish", although the name literally means horned goat.
The constellation is ancient, and was one of the earliest members of the zodiac, perhaps transferred to the heavens from far older earthly concerns.
Horned animals, particularly the ibex, were worshipped icons in the prehistoric Near East, as seen on pottery as far back as 5500 BC. Often these animals appeared with pictorial representations of the 'Tree of Life' and lunar or astral symbols. That is, for thousands of years -- as attested by both pottery and cylinder seals -- this horned animal played a central part in some mythology which involved the heavens,culminating (perhaps around 2000 BC) with the sacrificial scenes depicted on Akkadian cylinder seals (below).

One respected student of the Near East, Professor Willy Hartner, late director of the Institut für Geschichte der Naturwissenschaften (Institute for the History of Natural Science) at the Johann Wolfgang Goethe-Universität in Frankfurt, has postulated that the ibex was an early constellation, which was later broken up to form Capricorn and Aquarius. [See "The Earliest History of the Constellations in the Near East and the Motif of the Lion-Bull Combat", Journal of Near Eastern Studies, Volume 24 (1965) pp 1-16.]

Hartner's Diagram 1a shows the heavens as they would have appeared in 4000 BC in Mesopotamia. He argues that a much larger constellation, The Ibex, was in place where we now have Aquarius and Capricorn.

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.

Deep Sky Objects in Capricornus:

The only Messier in the constellation is M30 (NGC 7099), a globular cluster about 40,000 light years away. It has a very concentrated centre, with a number of star chains (or strings) from the centre to the periphery.

M30 is 3º ESE of zeta Capricorni.

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