Jimmy Westlake: Auriga, the Charioteer
November 16, 2015
What's that flashy, golden star hovering over the northeastern mountains as darkness falls in mid-November? It's Capella, the third brightest star visible in Colorado skies and the brightest star in our constellation of Auriga, the Charioteer.
Auriga represents a Greek mythological character named Erichthonius. He was born lame and invented the four-horse chariot so that he could get around more easily.
In the sky, he is shown holding a nanny goat and her three kids under his arm. The star Capella represents the nanny goat, and a cute little trio of stars close by represents "the kids."
Capella shines down on us with a yellow light almost identical to that of our sun but from a distance of 42 light years. This little nanny goat is hiding a secret that only modern astronomers have been able to unravel.
Capella is really two yellow giant stars in a close orbit around each other. The stars are separated by about the same distance between Venus and the sun, and they whirl around each other once every 104 days.
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Much farther out, a pair of faint red dwarf stars orbits around the yellow giant pair with a period of several thousand years. Capella is a wonderful example of a quadruple star system. To the naked eye, however, she gleams as a single star.
Capella is the brightest star close to the north celestial pole and, as such, remains above the horizon 24/7 for folks living north of the latitude of Yellowstone National Park. For Coloradoans, Capella is up for 20 hours a day, hiding behind our northern mountains for four hours each day before rising again in the northeast.
The star Elnath at the southern-most corner of Auriga's distinctive pentagon of stars actually belongs in the neighboring constellation of Taurus the Bull but has always been associated with Auriga. To the ancient sky watchers, this star represented both the foot of the Charioteer and the horn of the Bull at the same time. Modern astronomers found this duality unacceptable and officially ceded Elnath to Taurus.
Auriga is loaded with interesting celestial objects. Within his borders lie three beautiful star clusters, known by their Messier catalog numbers, M36, M37 and M38. They are visible to the unaided eye on a dark, clear night but use binoculars or a small telescope for the best view.
The star at the top of the triangle marking "the kids" is a most unusual object, known as Epsilon Aurigae or Al Anz. This eclipsing binary star holds the record for having the longest time between eclipses — 27 years — but what makes Epsilon even more remarkable is that its eclipse lasts for 670 days or nearly two years.
Whatever it is that blocks the main star from view must be enormous in size. Recent studies have revealed that a colossal dark cloud of gas and dust is what eclipses the central star. The next eclipse of Al Anz won't happen until the year 2036.
Professor Jimmy Westlake teaches astronomy and physics at Colorado Mountain College’s Alpine Campus. His “Celestial News” column appears weekly in Steamboat Today and his “Cosmic Moment” radio spots can be heard on local radio station KFMU. Check out Westlake's new "2016 Cosmic Calendar" of sky events on his website at http://www.jwestlake.com. It features twelve of his best sky photos and a day-by day listing of cool celestial events that you and your family can enjoy watching in 2016.
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