Jimmy Westlake: Cassiopeia's Chair


Summer is slipping away from us, and the changing constellations are a sure sign of the approach of autumn. The Big Dipper that rode high during the early evening in the spring and summer sky now is sinking into the northwest. The Summer Triangle, too, is beginning to migrate westward. A whole stage full of new constellation characters is rising in the east to take their places. What are all those new stars?

One of the first star patterns to catch your eye in the late summer and early fall sky is a distinctive group of five bright stars in the northeastern sky forming the shape of a letter "W," rotated counterclockwise on its side. Meet Cassiopeia, the Queen. The five stars of the W-pattern actually form the outline of the Queen's chair, hanging upside down in the sky. Why upside down?

Greek mythology explains that Cassiopeia is being punished for her boastful ways. 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 would spend 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 closest of Cassiopeia's five main stars at a distance of 54 light years, while the star marking the middle of the W is the most distant at 613 light years. This star, simply referred to as 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. For example, in 1937, Gamma briefly brightened to rival the brightest stars in the sky, then faded to a very unimpressive third-magnitude star before returning to its present second-magnitude status.

From Colorado, Cassiopeia is a circumpolar constellation, meaning that it never actually sets below the northern horizon, but just barely skims above the mountaintops to the north before rising high again. She is diametrically opposite the Big Dipper with respect to the North Star, Polaris, so one or the other star pattern is visible all year long. 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 area of Cassiopeia, check out that fuzzy patch of light just east of the star Segin. It's the famous "Double Star Cluster," and it is beautiful through binoculars!

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 on the websites of CNN.com, NASA's "Astronomy Picture of the Day" website, Spaceweather.com, Space.com, Discover.com, MSNBC.com, NationalGeographic.com, and in Sky & Telescope, Astronomy, Night Sky, Discover, and WeatherWise magazines.


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