Jimmy Westlake: Cassiopeia ushers in autumn
August 26, 2013
Summer is slipping away, and the changing constellations are a sure sign of autumn's approach. The Big Dipper that rode high in the sky during spring and summer evenings now is sinking into the northwest. The Summer Triangle, too, is migrating westward. A whole cast of new celestial characters is rising in the east to take their places.
One of the first star patterns to catch your eye in the late summer and early fall is a distinctive group of five bright stars in the northeastern sky forming the shape of the letter "W." This familiar pattern represents Cassiopeia, the ancient Ethiopian Queen. The five stars of the W-pattern actually form the outline of the Queen's throne, hanging upside down in the sky. Why upside down?
Greek mythology explains that Cassiopeia is being punished for boastful arrogance. She had a bad habit of doting on her beautiful daughter, Andromeda, and once went so far as to claim that Andromeda was more beautiful than the sea nymphs, who were the pride and joy of Poseidon, the mythological god of the sea. Poseidon punished Cassiopeia by placing her in the sky close to the pole star so that, as she rotates around the pole, she spends half of the year upside down, clinging to her throne for dear life. Let this be a lesson to all the vain and boastful people out there.
The star Caph, at the top of the W, is the nearest of Cassiopeia's five main stars at a distance of 54 light-years from Earth, while the star marking the middle of the W is the most distant at 613 light-years. This middle star, simply referred to by its Greek letter designation Gamma, is the brightest unnamed star in the northern hemisphere. Perhaps it was much fainter centuries ago when the Greeks and Arabs were naming the stars. Gamma is known today to be an unpredictable variable star that occasionally increases dramatically in brightness. Most recently, in 1937, Gamma brightened briefly to rival the brightest stars in the sky, then faded to its present second magnitude status.
From Northwest Colorado, Cassiopeia is a circumpolar constellation, which means that it never dips below the northern horizon. It barely skims over the mountaintops to the north before rising high again.
Cassiopeia's chair is diametrically opposite the North Star, Polaris, from the Big Dipper, so one or the other star pattern is visible at all times. While the Big Dipper dominates the spring sky, Cassiopeia rules the autumn nights. Just follow the hazy band of the Milky Way northward to find that familiar W-shaped pattern of Cassiopeia.
And while in the vicinity of Cassiopeia, check out that misty patch of light just east of the star Segin at the left tip of the "W." It's the famous Double Star Cluster, also called h and Chi Persei, and it is spectacular when seen through binoculars!
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 Westlake's astrophotography website at http://www.jwestlake.com.
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