mercredi 3 septembre 2008

Argo Navis 2 Carina


This is one of the parts into which the ancient Greek constellation of Argo Navis, the ship of the Argonauts, was divided by the French astronomer Nicolas Louis de Lacaille in his catalogue of the southern stars, Coelum australe stelliferum, published in 1763. Although usually described as the keel, Carina represents the main body of the ship. It contains the second-brightest star in the entire sky, Canopus, a creamy white giant just over 300 light years away, that marks one of the ship’s two steering oars.
Canopus is not mentioned by Aratus, because the star was below the horizon from Greece in his day; the name first appears with Eratosthenes who worked farther south, at Alexandria in northern Egypt, and hence would have seen it. Greek writers such as Strabo and Conon tell us that Canopus is named after the helmsman of the Greek King Menelaus. On Menelaus’s return from Troy with Helen his fleet was driven off-course by a storm and landed in Egypt. There Canopus died of a snake bite; Helen killed the snake, and she and Menelaus buried Canopus with full honours. On that site grew the city of Canopus (the modern Abu Qir) at the mouth of the Nile. Fittingly, modern space probes now use Canopus as a navigation star. Eratosthenes also knew this star by the name Perigee, in reference to the fact that it remained close to the horizon.
The constellation contains a unique star, Eta Carinae, that flared up to become brighter than Canopus in 1843, but has since faded to the limit of naked-eye visibility. Astronomers think that it is a young, massive star that will one day explode as a supernova.

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