The distinctive pentagonal outline of the constellation Auriga, the Charioteer, rises over the northeast horizon at about 8 p.m. in mid-November. Look for the bright star Capella and her three “kids” leading the way.
Jimmy Westlake's Celestial News column appears Tuesdays in the Steamboat Today.
Find more columns by Westlake here.
What’s that twinkly, 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 the constellation of Auriga, the Charioteer.
Auriga represents the mythological character Erichthonius, who was born lame and invented the four-horse chariot so 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 nearby represents “the Kids.”
Capella shines down on us with a yellow light almost identical to that of our sun from a distance of 42 light years, but this little nanny goat is hiding a secret that only modern astronomers have been able to reveal. Capella is really two yellow giant stars in a close orbit around each other. The stars are separated by about the same distance between our planet Venus and the sun, and they whirl around each other once every 104 days. Much farther out, a pair of faint red dwarf stars orbits around the pair of yellow giants with a period of several thousand years. Capella is a wonderful example of a quadruple star system, though to the naked eye she gleams as a single star.
Capella is the closest bright star to our north celestial pole and, as such, remains above the horizon continuously for folks living farther north than Yellowstone National Park. For Coloradans, Capella dips below our northern mountains for just a brief time 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 Taurus the Bull but always has 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 dual personality unacceptable and officially ceded Elnath to Taurus.
The band of the Milky Way runs right through Auriga, so it is chock-full of 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 very unusual object. Known as Epsilon Aurigae, this eclipsing binary star holds the record for having the longest time between eclipses — 27 years. For comparison, the nearby “Demon Star,” Algol, has an eclipse every 2.9 days. What’s even more remarkable is the duration of Epsilon’s eclipse — 670 days. Whatever it is that eclipses the main star must be gigantic in size in order to cover it up for so long. Recent studies have revealed a colossal dark cloud of gas and dust eclipsing the star. Epsilon just emerged from its most recent eclipse this past spring, so it will continue to shine steady for the next 25 years.
Jimmy Westlake teaches astronomy and physics at Colorado Mountain College’s Alpine Campus. He is an avid astronomer whose photographs and articles have been published all around the world. Visit his website at www.jwestlake.com.