Re: What is difference between constellation and a star group?

Hi Bruce

A constellation is a group of stars which if you connect the stars with lines, form a figure in the sky of an object, hero, or animal. There are 88 standard constellations recognized by astronomers. The International Astronomical Union is responsible for setting the boundaries within each constellation. Constellations are useful reference points to use when directing people where objects are in the night sky. It is of interest that in the past, different cultures seemed to have their own constellations based upon their own special legends and mythology. In some cultures separated by time and distance, they have the same names for the same constellations.

Star Groups or as they are more commonly called, Star Clusters are totally different. One type is called an Open Cluster or Galactic Cluster. The Pleiades is an example of this type of cluster. They receive their name from their tendancy to be found inside the Milky Way Galaxy (our home galaxy) along the spiral arms and from their loose, scattered appearance. The other type of cluster is called a Globular Star Cluster. It is circular in appearance, much richer in stars, and and more compact than an Open Cluster. Some say it resembles a spherical swarm of celestial bees. An example is Omega Centauri which contains about a million stars and is about 200 light years in diameter. It shines with the luminosity of about 500,000 times the luminosity of our sun.

A great book of the constellations is "Observing The Constellations" by John Sanford ISBN 0 671 68924 X. You can buy it at most large bookstores.