vendredi 12 septembre 2008

Corona Borealis 5

Or the Northern Crown, is the crown Ariadne wore at her wedding. It was made by the supreme goldsmith, Hephaestus, at his underwater smithy.
The story is connected to a more notable myth, of the Minotaur and of Theseus, who was destined to kill it. To do so, he needed Ariadne's help. This beautiful young maiden was the daughter of Minos, king of Crete. She was also the half-sister to the Minotaur, the half-man half-bull which lived at the centre of a labyrinth.
Every year Minos ordered seven young men and seven maidens from Athens to be served up to the Minotaur. The current hero in Athens was Theseus, son of Poseidon, and heir to the Athenian throne. Only a young man, Theseus had already proved himself by a variety of heroic deeds. Then time came for the yearly tribute to Crete. Theseus volunteered to be one of the seven young men.
As he arrived in Crete, Theseus was met by Minos, who challenged the young man to prove he was indeed the son of Poseidon. Minos threw a gold ring into the sea, and told Theseus to fetch it.
Theseus dove into the deep, and was met by dolphins which escorted him to the palace of the Nereids. Thetis, one of the Nereid sisters (or sea nymphs), gave Theseus a jewelled crown that Hephaestus had made. With the gold ring and the crown, Theseus swam back to Crete. This feat received the loving admiration of Ariadne.
Ariadne had a magic ball of twine that could roll out by itself and follow the path to the centre of the labyrinth, where the Minotaur was kept. She promised to help Theseus kill the Minotaur if he would marry her and take her back to Athens. Theseus agreed, so she gave him the ball of twine. Theseus followed the rolling twine to the centre of the labyrinth and promptly killed the Minotaur.
Unfortunately he forgot his promise. Or, some say, he did marry Ariadne, giving her the jewelled crown as a wedding present. And then he later abandoned her on the isle of Naxos, on the way to Athens.
Others have it that Theseus sailed off, leaving a sleeping Ariadne to pine for her loss. She implored her father, Zeus, to make amends. Zeus took pity and sent Dionysus to comfort his daughter.
Another version has Dionysus visiting Naxos and falling in love with Ariadne, so he cast a spell on Theseus. Theseus then forgot all about Ariadne and sailed off for Athens. In any case, Dionysus took her for his bride and placed the jewelled crown of Hephaestus on her head.
They raised four sons and `lived happily ever after'. When Ariadne died Dionysus took the wedding crown and placed it in the heavens between Hercules and Bootes.
The constellation Corona Borealis is found nearly midway between Arcturus and Vega; a little closer to the first of these stars. From Arcturus move up to Izar (epsilon Bootis) and then east fifteen degrees to alpha CrB.
The seven stars that make up the crown are not terribly bright, except for Gemma, or Alphecca (alpha Coronae Borealis), which is a 2.2 magnitude star 75 light years away.
The rest of the Bayer stars vary from three to six magnitude. The constellation includes several fine binaries, an unusual variable, and an extremely faint cluster of galaxies.
Both alpha Coronae Borealis and beta Coronae Borealis are spectroscopic binaries, with periods of 17.36 days and 10.5 years respectively.
Gamma CrB is also a spectroscopic binary (period uncertain) as well as a very close visual binary (see below).
Zeta CrB is actually two stars which form a splendid binary (see below). The two are approximately 220 light years away, given their parallax of 0.015".
Double stars in Corona Borealis:
Gamma CrB (Struve 1967) is a close binary with an orbit of 91 years. The PA is 265º and separation about 0.2".
Eta CrB (Struve 1937) is a fine binary with orbit of 41.5 years. Presently the companion can be found at PA 47º and separation 0.9".
Zeta2 and zeta1 CrB (Struve 1965): a pleasant pair of blue-white stars with 5.0 and 6.0 magnitudes; PA 305º, separation 6.3". Note that zeta2 is the primary.
Sigma CrB (Struve 2032) is a slow binary, with a period of a thousand years. Currently the companion is at PA 236º and separation 7.03"
Nu1 and nu2 CrB (Struve I 29) form a very wide (but only optical) pair of orange giants, quite suitable for binoculars: PA 166º, separation 372".

Aucun commentaire: