jeudi 4 septembre 2008

Auriga 6

Is an ancient Northern Hemisphere constellation featuring one of the brightest stars in the heavens: Capella. Auriga is usually pictured as a charioteer; the youth Auriga wields a whip in one hand and holds a goat (Capella) and her two kids in the other.
Capella means "small goat". A previous name of this star was Amalthea, which was the goat that suckled the baby Zeus. There are many ancient stories relating to the star, as every culture in antiquity found a place for this bright companion to Taurus, its closest neighbour. To find Auriga, first locate Orion. Taurus is to the right (west) and just above these two, much higher in the sky, you will see Capella. While this star marks roughly the mid-point of the constellation, north to south, most of the more interesting aspects of the constellation are found to the south of the star, all the way down to El Nath, the second brightest star (gamma Aurigae) which is actually shared with Taurus, and also known as beta Tauri.
Auriga's stars are fairly bright; five are second magnitude or brighter. Alpha Aurigae (Capella) is the sixth brightness star, at a visual magnitude of 0.08. The star is 43.5 light years away, and is about ten times the size of our Sun.
Capella's visual magnitude is really the combined brightnesses of the primary star and a close companion, that revolves every 104 days. There is another companion, much fainter: a red dwarf which is itself a close binary.

Binary stars in Auriga.
Zeta Aurigae is an eclipsing binary; an orange giant primary with a blue companion that orbits every 972 days (2.7 years).
Theta Aurigae is visible in large scopes: 2.6, 7.1; PA 300º and separation 3.6".
Omega Aurigae: 5.0, 8.0; PA 360º, separation 5.4".
14 Aurigae is a multiple double, visible in larger scopes.
The primary is 5.1, with three companions: B (11.1, 352º, 11"), C (7.4, 225º, 15") and D (10.4, 356º, 7.7").

Variable stars in AurigaThere are a half-dozen variable stars in this constellation which are visible in small scopes, most of them of very small variance.
Epsilon Aurigae is an unusual variable which normally maintains a visual magnitude of 2.92 but every 9892 days (27 years) dips down to 3.83.
The next scheduled dip is in the late summer of 2010. The eclipse phase lasts about a year.
R Aurigae is the only Mira-type variable of interest. Normally a rather faint 6.7, every 457.5 days it takes a nose-dive to 13.9. The best time to view this feature is in late November of 2001, when it should be near the transit.

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