Jimmy Westlake: Two bright stars of autumn
October 21, 2013
Steamboat Springs — The autumn sky is remarkably devoid of bright stars. During the early evening hours of a winter's night, you can see eight of the sky's 20 brightest stars. By springtime, that number has grown to 10 and, by summer, it has dwindled to only six.
In early autumn, the number of bright stars has been reduced to five. That includes the three bright stars of the Summer Triangle asterism, Vega, Deneb, and Altair, soaring high in the western sky and still hanging on after our summer has ended. The two bright stars that are specifically associated with the season of autumn are Fomalhaut (pronounced fo-ma-low) and Capella.
These two bright stars of autumn rise above our mountains at about the same time, Fomalhaut in the southeastern sky and Capella in the northeastern sky.
Let's start with Fomalhaut. Located only 25 light years from Earth, blue-white Fomalhaut marks the opened mouth of Piscis Austrinus, the Southern Fish, as he gulps down the stream of water pouring from the water jug of Aquarius, positioned above. It is the 17th brightest star visible from Earth but seems much brighter because it lies in a rather blank region of the southern sky where it reigns supreme.
In 1983, an orbiting infrared telescope named IRAS discovered a thick ring of icy dust particles surrounding Fomalhaut. Astronomers theorize that our own planetary system formed from just such a ring of debris around the nascent sun.
In 2008, the Hubble Space Telescope discovered a large Jupiter-like planet, Fomalhaut-b, orbiting just inside the inner edge of the ring. Although nearly 1,000 planets have been detected around other stars, Fomalhaut-b has the distinction of being the first one to be directly imaged.
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Turning now to the northeastern sky, we see Capella, a beautiful yellow star belonging to the constellation of Auriga the Charioteer and located about 42 light years from Earth. It is the sixth brightest star visible in our sky. Her name means "the She-Goat," and she has the distinction of being the northernmost of the 20 brightest stars and the closest to the north celestial pole.
A tiny triangle of stars near Capella represents her three kids. Capella appears to the eye as a single star, but looks can be deceiving. The point of light that we see as Capella is actually a pair of nearly identical stars that orbit each other once every 104 days.
Watch for Fomalhaut and Capella, the two bright stars of autumn, around 8 p.m. in late October.
Professor Jimmy Westlake teaches astronomy and physics at Colorado Mountain College’s Alpine Campus. His “Celestial News” column appears weekly in the Steamboat Today newspaper and his “Cosmic Moment” radio spots can be heard on local radio station KFMU. Check out Jimmy's astrophotography website at http://www.jwestlake.com.