For thousands of years, stargazers have seen shapes in the night sky. Some of
these visions, like the mythological creatures of the zodiac, are said even
today to guide the course of human destiny. While the predictions of astrology
may be dubious, star patterns can still be our guides. These figures help us
navigate our way across the night sky and locate celestial objects.
Star patterns such as the hunter Orion and the winged horse Pegasus are
commonly called constellations. But the term constellation in modern astronomy
actually refers to a particular region of the sky, like a country on a map. The
star figures first noticed in antiquity lie within these regions.
A Ladle? Or A Bear?
Some constellations hold other identifiable shapes formed by stars, called
asterisms. Seven bright stars within the constellation Ursa Major form what may
be the most renowned asterism through the ages. This shape has been noted by
poets from Homer to Tennyson, and known variously as the Plough, the Wain, and
the Wagon. Today, we call it the Big Dipper.
By connecting stars in the constellation Ursa Major in a different way, you can
see the rough shape of a bear. Ursa Major means "Great Bear" in Latin, but many
civilizations have given this asterism their own name for bear. It was
"Arktos" to the ancient Greeks. (The word "arctic" today relates to the
connection between these circumpolar stars and northern latitudes.) And some
Native American tribes saw three hunters in nearby stars chasing the bear
around the northern sky.
The shapes we draw may vary, but the borders of the constellations are fixed.
In 1930, astronomers divided the sky into 88 constellations, giving each a
Latin name. Before this time, there was no one universally accepted sky map,
and quite a lot of confusion.
To see some of the constellations that are home to newly discovered solar
systems, go to Find the Planets.
Ursa Major images courtesy Sky and Telescope Magazine.