Constellations are often defined as a pattern of stars but that's a little like defining Vermont as the line of towns running from Burlington to Montpelier, or New Hampshire as Concord-Manchester-Nashua, or New Jersey as — well, I have friends in New Jersey.

Like states, constellations are defined as areas mapped out on the sky or, more precisely, as volumes of space extending down to the observer on Earth. An asteroid tumbling past our planet may have no relation to the distant stars for example, but it is quite proper to describe it as moving through the constellation of Pegasus.

While we define constellations in terms of area or volume, it is still the patterns of stars that attract our imagination. Pegasus represents the winged horse of Greek mythology and perhaps in the days before large cities, streetlights, and smog, it was easier to see a horse in that pattern of stars. I find it hard to make out a horse but it's easy to see the four stars that mark Pegasus' body.

To identify the Great Square of Pegasus, face south on a clear evening. Between 10 and 11 pm, the moderately bright stars of the Great Square will be nearly overhead. Lines of fainter stars stretching from the stars on the right represent the horse's head and legs.

Look carefully at the upper left star of the Great Square, a star named Alpheratz. Two strings of stars stretching to the upper left represent the princess Andromeda. Alpheratz has the odd distinction of having belonged to two constellations. Modern boundaries zig to include it in Andromeda where it sparkles as a jewel in the princess' crown but it has long been a part of Pegasus as well. The star's name derives from its Arabic name meaning "mare's navel."

If ancient astronomers had drawn the horse differently, that star might have had a very different name.

Andromeda's most famous feature (I refer to the constellation, not its namesake) is the Milky Way's most impressive neighbor, the Andromeda Galaxy. It is home to perhaps a trillion stars, more than double the number in our home galaxy. In a clear, dark sky, the Andromeda Galaxy is visible to the unaided eye as a faint patch of light, the most distant object visible without telescope or binoculars. If you see it tonight, your eyes will collect light that left the galaxy's stars two and a half million years ago.

If you dress warmly and brave the evening chill under a clear sky, look for other jewels. The Milky Way will arc overhead. Three bright stars, the so-called Summer Triangle of Deneb, Vega (the brightest of the three), and Altair (the closest to the horizon), will be slipping toward the northwest hills. Orion the Hunter will be climbing above the eastern horizon and, just above Orion's head, Jupiter will blaze with a cool silvery light.