vendredi 19 septembre 2008

Hydra 4

Like a number of other constellations, the Hydra concerns the story of Heracles' labours. This time it is the Second Labour of Heracles.
Having killed the Nemean Lion, and wrapping the protective pelt around himself, Heracles set off to find the Hydra. This was a gigantic dog-like beast with many heads. Some say it had seven, others as many as fifty. Euripides, with characteristic exaggeration, gave it ten thousand heads.
Seven is usually the accepted number, possibly because of the seven rivers in this part of the Peloponnesian peninsula, tributaries of the river Amymone.
At any rate, one of these heads was immortal, which meant the beast was immortal. Its breath was deadly and if one even smelled its tracks, he would die.
With the help of Athene, Heracles locates the monster's lair and soon he is in a life and death struggle with the beast. Heracles slices off one of the monster's heads, only to see a couple more grow in its place.
Heracles calls out to his chariotter Iolaus for help. Iolaus sets the grove on fire and then begins cauterizing the bleeding stumps. With the blood flow stopped the Hydra's heads cease to multiply.
Finally Heracles cuts off the immortal head and - as it is still furiously hissing away - he promptly buries it under a huge rock. He cuts up the rest of the Hydra's body and dips all his arrows in the dead monster's gall. The slightest scratch from one of these arrows would bring instant death.
While one might be tempted to say "well done", Eurystheus (who had assigned these labours to Heracles) was not satisfied. Heracles had cheated, he said, since he had needed Iolaus' assistance.
One might wonder just why Heracles had been forced to do all these labours. Before either he or his twin were born, Hera decided that Eurystheus rather than Heracles should become the king of Mycenae. So she hastened his birth; Eurystheus was born two months premature. And Heracles, being the younger of the two, became subservient to Eurystheus.
Thus born premature, this king of Mycenae was weakly and timorous. He commanded Heracles to perform twelve labours in twelve years in order to keep him away from his own kingdom, afraid Heracles would take his throne. Eventually he would be killed by either Heracles' son (Hyllus) or by his charioteer, Iolaus.
As a constellation Hydra sinuously winds down from the northern hemisphere, bordering Cancer, to as far in the southern hemisphere as Centaurus, stretching out to around one hundred degrees in the process. At one point its body is actually cut off by another constellation (the southwestern tip of Crater).
Although the constellation is best seen in March and April, its brightest star, alpha Hydrae, transits on 12 February. Slowly over the next few months the Hydra then slithers over the skies earlier and earlier.
To find Hydra, locate Regulus (alpha Leonis). Now drop straight down twenty degrees, passing through the uninspiring constellation of Sextans. The bright star to the west is Alphard (alpha Hydrae).
You've just found the "heart" of the Hydra. To find its head, look for the compact stars to the northwest. It is easiest to do this with the naked eye, or with binoculars. These stars are not quite as far north as Regulus.
The tail of the monster stretches far to the east, even past Spica (alpha Virginis). You'll have to wait until the small hours of the morning to see these stars, or until later in the spring when they appear at a more reasonable hour.
There are a number of interesting deep sky objects, including two Messier objects, and several very nice double stars. All in all, Hydra's stars are of average brilliance, except for Alphard (alpha Hydrae).
Alphard is a bright giant, about 25 times the Sun's diameter. Its distance is 89 light years, and it has a luminosity of 95 Suns.
The Arabs called the star "Al Fard al Shuja" (The Solitary One in the Serpent) while later on Tycho Brahe named it "Cor Hydrae" (The Hydra's Heart).
Beta Hydrae is the southern-most star of any importance. Quite dim for its name, the star is a visual binary (see below).

Aucun commentaire: