Asterisms Outline Some of the Brightest Constellations

by Rod Kennedy

Most people are at least familiar with the names of a few constellations.   If asked to name one they usually say, “The Big Dipper.”  However, the Big Dipper is not a constellation.  It is instead an asterism, a group of stars that are bright and easy to recognize but that are part of a larger constellation.  For people living under light-polluted skies, asterisms may be all they see of the constellations.  August is a great time to see some bright asterisms, and in the process learn the constellations they belong to.

The best known, and easiest to see asterism is the Big Dipper.  This asterism lies low in the northwest in August, slowly turning its way toward the northern horizon.  This asterism is part of the constellation Ursa Major, the Great Bear.  Using the first two stars in the bowl of the dipper, we can find our way to the star Polaris, which is the North Star.  Polaris is also the tip of the handle of the asterism known as the Little Dipper.  Like the Big Dipper, the Little Dipper is part of a bear constellation, in this case Ursa Minor, the Little Bear.  Directly east of  Polaris is the W of Cassiopeia the Queen.  Looking to the west of the Big dipper is the Kite, which is part of Boötes the Herdsman.  The Kite is easy to find if you follow the curve of the Big Dipper’s handle to the bright orange star Arcturus.

Some asterisms are composed of more than one constellation.  Looking almost directly overhead we find the three bright stars Vega, Altair and Deneb.  These stars form the asterism known as the Summer Triangle.  These stars are the brightest stars in the constellations Lyra the Harp, Aquila the Eagle, and Cygnus the Swan.  Cygnus the Swan also contains an asterism.  By removing the ends of the wings we find the bright central stars that form the Northern Cross.  Between the Summer Triangle and the Kite is an asterism known as the Keystone, which represents the body of Hercules the Strongman.  Just above the Keystone is another keystone shaped asterism called the Lozenge which represents the head of Draco the Dragon.

Looking south we find the Fish hook asterism. For constellation purists the Fish hook is the tail of Scorpius the Scorpion.  Following behind the Fish Hook is the Teapot.  The Teapot is very easy to see, much like the Big Dipper.  Just as the Big Dipper is the most visible part of Ursa Major, the Teapot is the most visible part of Sagittarius the Archer.
The last asterism that is visible in August appears on the eastern horizon after ten pm.  This asterism is the Great Square, better known as Pegasus.

For observers living under light-polluted skies, many of the constellations are very difficult to see and identify.  Fortunately most of them are composed of at least a few very bright stars that form an easy to see pattern.  These patterns, known as asterisms are a great way to learn your way around the sky as well as find and identify the constellations.  Those lucky enough to be under very dark skies get the rare pleasure of seeing the asterism as well as the constellations in glorious beauty against the dark of the night.

August 2012 Chart

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