After the Big Dipper and Orion's Belt, Cassiopeia is probably the next most familiar star pattern — at least for northern hemisphere skywatchers. If you live in the opposite half of the globe, the Southern Cross comes to mind.
Cassiopeia represents a queen sitting on a throne holding a mirror, but to the casual observer looks like the letter W. In early summer the W rests horizontally low in the northern sky. But by late August it tips up on one end in the northeast. The three stars at the top of the constellation are as bright as the Big Dipper stars and quickly get our attention. Two fainter stars fill out the figure.
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I like to use the three bright ones, which form a nifty triangle, to point me to the Andromeda Galaxy, one of the most distant objects in the heavens visible with the naked eye. Binoculars make it much more obvious. Either way, it appears as an elongated, smoky streak with a brighter center. The galaxy is home to a trillion stars, all of which blend together at its enormous distance into an amorphous haze.
The bottom stars of the W will direct you to the Double Cluster in the nearby constellation Perseus the Hero. It and all the stars we see in the night sky belong to the Milky Way Galaxy, which is shaped something like a pinwheel. This unique pair of side-by-side star clusters is located about 7,500 light-years away in one of the galaxy's outermost whorls called the Perseus arm.
Despite its remoteness, the Double Cluster is visible without optical aid as a fuzzy spot from dark, moonless skies. If you have binoculars, don't pass up the chance to zero in. Unlike Andromeda, you'll be able to make out lots of faint, shimmering stars in and around the two clusters.
Each is a separate, gravitationally-bound group of suns several hundred light-years apart that just happen to lie along similar lines of sight — the reason they appear so close together. The W and surrounding area is packed with additional star clusters well worth hunting in binoculars from rural skies. Most look like small, fuzzy spots occasionally speckled with tiny stars. The band of the Milky Way runs through Cassiopeia, so when we look in its direction we peer through the richest, densest part of the galaxy. No wonder we spy so many treasures there.
Cassiopeia climbs higher and higher as the night advances, reaching its greatest elevation in the northern sky directly above the North Star around 3:30 a.m. local time in late August. That's when you'll notice a funny thing has happened — the W has spun around and now looks like an M.
Although the outline of Cassiopeia has been nearly constant for hundreds of years, all of its stars, which lie at different distances from Earth, are moving about the center of the galaxy. Typical star speeds are in the neighborhood of 60 miles per second (100 km/sec). That can only mean one thing. In time, the constellation's outline will slowly grow distorted and ultimately become unrecognizable. Our remote descendants will see a "new" constellation in its place . . . and this article will require a thorough update!
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