Jimmy Westlake: Cassiopeia ushers in autumn
August 24, 2015
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 the spring and summer evenings is now sinking low into the northwest. The Summer Triangle, too, is migrating westward. A whole new cast of 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 5 bright stars in the northeastern sky that forms the shape of a letter W. This familiar star pattern represents the chair or throne of Cassiopeia, the Queen, hanging upside down in the sky. Why upside down?
Greek mythology explains that Cassiopeia is being punished for her 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, the daughters of Poseidon, the mythological god of the sea. ‘
Poseidon was furious at this boasting. He punished Cassiopeia by placing her in the sky close to the pole star so that, as she circles the pole, she spends half of the year upside down, clinging to her throne for dear life. At least, that's the story that's been told for over 2,000 years.
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The star at the top of the W, Caph, 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 550 light years. This middle star, simply referred to by its Greek letter designation Gamma Cas, is the brightest unnamed star in the sky's northern hemisphere.
How did this happen? Maybe it was much fainter centuries ago when the Greeks and Arabs were naming the stars.
Gamma is known to be an unpredictable variable star that occasionally flares up dramatically in brightness. Most recently, in 1935, Gamma brightened briefly to rival the brightest stars in the sky, then, it faded to its present second magnitude status. It has undergone a slow brightening for the last several decades and is now the brightest it has been in nearly 80 years. We'll just have to wait and see what Gamma Cas has in store for us next.
From Northwest Colorado, Cassiopeia is a circumpolar constellation, which means that it is above our horizon 24/7 and never sets. It barely clears 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 stunning when seen through binoculars or a small telescope.
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.