At its most general, the word “constellation” refers to a group of celestial bodies which appear to form a pattern in the sky.  Not all familiar, easily-recognized patterns are constellations.  For instance, the Big Dipper isn’t a constellation, although it is (coincidentally) part of a constellation.  The Big Dipper is a “stand alone” pattern called an asterism.

NGC 290 Star Cluster, NASA/ESA HubbleSite

Many people think of the Zodiac when they think of constellations, but that’s fairly limiting.  The Zodiac (used in Astrology) consists of only the twelve constellations that roughly line the ecliptic.  Since 1922, the International Astronomical Union has recognized 88 constellations.  The ancient Greeks were familiar with more than half of these, and some archaeologists now believe that our ancestors were depicting on cave walls the patterns they saw in the night sky some 17,000 years ago.  While it’s not possible to know what meaning (if any) prehistoric man attributed to these patterns, the drawings themselves are believed to have been of religious or social importance.

Path of the point of vernal equinox along the ecliptic over a 6000 year period - Image D.Bachmann, all rights reserved

In early Greek and Roman civilizations, knowing the constellations could prove to be very important.  Before the invention of the compass, the only way you could navigate (by land or by sea) was by studying the positions of familiar celestial bodies; the Sun, the Moon, the stars, the constellations.  Linking the constellations to stories of heroes, villains, monsters, and exciting legends made them more familiar; easier to recognize and remember.  The legends themselves usually contain “add on” stories telling how that particular subject came to be a constellation; for example, Cancer the crab was made a constellation by the goddess Hera, who sent him to distract Hercules while he was fighting the Hydra.  Cancer was stomped to death, but Hera made him a constellation as a reward for his effort and sacrifice.

I’m sure that made Cancer feel tons better about being stomped to death by Hercules.

There are about 35 “former” constellations that, for one reason or another, didn’t make it on the IAU list of 88 recognized constellations.  Some of these are well-known (Argo Navis – as in Jason and the Argonauts), and some not (Machina Electrica – yes, an electric generator).

Bode, Machina Electrica - Image Credit Michigan State University, Physics and Astronomy Dept

Whatever importance we give the constellations in modern science or philosophy, every human culture has them.  Even the Australian Aboriginal culture, the oldest continuous culture in the world, has an astronomical tradition.  We have always looked to the night sky, found our friends, and told stories about their adventures.

This is the website for the International Astronomical Union, linking directly to the page with the chart of all the constellations (the 88 recognized).  It gives you a star chart of each to view, one to download, and boundary coordinates for each constellation.

If you’re interested in reading the stories behind the constellations, this link will take you to Ian Ridpath’s Star Tales.  A very interesting read, and well worth looking over.