mercredi 3 septembre 2008

Bootes 5

This constellation (pronounced Boh-oh-tease) is closely linked in legend with the Great Bear, Ursa Major, because of its position behind the bear’s tail. The origin of the name Boötes is not certain, but it probably comes from a Greek word meaning ‘noisy’ or ‘clamorous’, referring to the herdsman’s shouts to his animals. An alternative explanation is that the name comes from the ancient Greek meaning ‘ox-driver’, from the fact that Ursa Major was sometimes visualized as a cart pulled by oxen. The Greeks also knew this constellation as Arctophylax, variously translated as Bear Watcher, Bear Keeper or Bear Guard.

According to a story that goes back to Eratosthenes, the constellation represents Arcas, son of the god Zeus and Callisto, daughter of King Lycaon of Arcadia. One day Zeus came to dine with his mistress’s father Lycaon, an unusual thing for a god to do. To test whether his guest really was the great Zeus, Lycaon cut up Arcas and served him as part of a mixed grill (some say that this deed was done not by Lycaon but by his sons). Zeus easily recognized the flesh of his own son. In a burning rage, he tipped over the table, scattering the feast, killed the sons of Lycaon with a thunderbolt, and turned Lycaon into a wolf. Then Zeus collected the parts of Arcas, made them whole again and gave his reconstituted son to Maia the Pleiad to bring up.
Meanwhile, Callisto had been turned into a bear, some say by Zeus’s wife Hera out of jealousy, or by Zeus himself to disguise his paramour from Hera’s revenge, or even by Artemis to punish Callisto for losing her virginity. Whatever the case, when Arcas had grown into a strapping teenager he came across this bear while hunting in the woods. Callisto recognized her son, but though she tried to greet him warmly she could only growl. Not surprisingly, Arcas failed to interpret this expression of motherly love and began to chase the bear. With Arcas in hot pursuit, Callisto fled into the temple of Zeus, a forbidden place where trespassers were punished by death. Zeus snatched up Arcas and his mother and placed them in the sky as the constellations of the bear and the bear-keeper. The Greek poet Aratus visualized Boötes as a man driving the bear around the pole. Later astronomers have given Boötes two dogs, in the form of the neighbouring constellation Canes Venatici.
A second legend identifies Boötes with Icarius (not to be confused with Icarus, son of Daedalus). According to this tale, recounted at length by Hyginus in Poetic Astronomy (II.4), the god Dionysus taught Icarius how to cultivate vines and make wine. When he offered some of his new vintage to shepherds, they became so intoxicated that their friends thought they had been poisoned, and in revenge they killed Icarius.
His dog Maera fled home howling and led Icarius’s daughter Erigone to where his body lay beneath a tree. In despair, Erigone hanged herself from the tree; even the dog died, either of grief or by drowning itself. Zeus put Icarius into the sky as Boötes, his daughter Erigone became the constellation Virgo and the dog became Canis Minor or Canis Major (according to different authorities).
Boötes contains the fourth-brightest star in the entire sky, Arcturus, mentioned by Homer, Hesiod and Ptolemy. Its name means ‘bear guard’ in Greek. Germanicus Caesar said that Arcturus “lies where his garment is fastened by a knot”, but Ptolemy placed it between the thighs, which is where mapmakers have traditionally depicted it. Astronomers have found that Arcturus is a red giant star about 25 times larger than the Sun, lying 37 light years away.

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