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Examples of Clusters and Galaxies

by Trevor Butler

There is a difference between objects that show stellar evolution and objects which are simply groups of stars. This page will talk about the type of objects that fall under groups of stars. There are two types of classifications: clusters and galaxies. Clusters also fall under two types, Open (or galactic) and Globular. Think of an open cluster as a town and a globular cluster as a city. If that analogy is true, then a galaxy is like a whole world.

Photo and Credits Type of star grouping


A portion of M44, an open cluster. Imaged by Trevor Butler using the New Mexico Skies 14" Celestron telescope.

NGC 1662, an open cluster. Most of the stars in this image are located in the same area. Imaged by the Astronomy and Physics research class using the New Mexico Skies 14" Celestron telescope.

 

Open clusters

Open clusters are within a galaxy, on a flat plane. The clusters are formed from emission nebulas. As the cluster gets older the stars move away from each other because there is no gravity to hold the stars in a group. As said above in the analogy, an open cluster is like a town. Some towns have hundreds of people and some have only a few people living in them. The same is true with open clusters; some have many stars while some have only a few stars.


M13, the great cluster in Orion. Imaged by Trevor Butler using the New Mexico Skies 14" Celestron telescope.

Globular clusters

A globular cluster is a cluster of stars like an Open Cluster but has a large number of stars in it. These clusters can be found in a halo outside a galaxy. Unlike the open clusters, a globular cluster is round, not located in the plane of the galaxy, and held together by gravity. The stars that make up the cluster are older than in an open cluster. The center of the cluster looks like a single giant star because the stars are so close together the light blends together in the picture, like in the picture at right.

M83, a Spiral Galaxy. Imaged by Trevor Butler using the New Mexico Skies 14" Celestron telescope. The view is called "face on."

M81, a Spiral Galaxy. Imaged by Trevor Butler using the New Mexico Skies 14" Celestron telescope.

M66, a Spiral Galaxy. Imaged by Trevor Butler using the New Mexico Skies 14" Celestron telescope.

M65, a Spiral Galaxy. Imaged by Trevor Butler using the New Mexico Skies 14" Celestron telescope. Notice the nearly edge-on appearance, indicating that spiral galaxies are flat.

Galaxies

Galaxies are large compilations of billions and zillions of stars. The galaxies spin, and the stars orbit within the galaxy. The center of a galaxy is denser with stars than the outer edge. There is a theory that at the center of most galaxies is a black hole because the black hole has a huge gravitational force. This galaxy is the Pinwheel Galaxy, and is much like ours. There are arms that extend like our galaxy. Our star, Sol, is located near the edge of one of the arms in our galaxy, the Milky Way.

 

 


Jeff Adkins, Director
astronomyteacher@mac.com

Cheryl Domenichelli, Assistant Director
cheryldomenichelli@antioch.k12.ca.us

4700 Lone Tree Way
Antioch, CA 94531

The ESPACE Academy is sponsored in part by a grant from the California Department of Education's Specialized Secondary Program.