Galaxies
You may be surprised to find out how many galaxies are in the universe. So many galaxies exist, that they are observed in clusters, like stars. The clusters can vary in both amount and density. Huge clusters with high densities are termed rich clusters. Other galaxies, like the Milky Way, are in local groups with small densities. These clusters is termed a poor cluster.
Each one of these galaxies contains billions, if not trillions, of stars, gas, and dust all held together by gravity. Astronomers have classified the galaxies into three main shapes. Learn about the different classifications of galaxies by clicking on each of images of galaxies in this interactivity.
Download a printable version of the interactivity above.
To learn more about the birth and evolution of galaxies, view the video Evolution of the Universe from eMediaVA℠. As you view the video, consider the following question: Which formed first - stars or galaxies?
The French astronomer, Charles Messier,
notable for publishing an astronomical catalog
Galaxy Names
Most galaxies are identified by a group of letters and numbers. These letters indicate the catalog listing of the galaxy. The galaxy could be listed in several different catalogs. The most common is NGC. This stands for New General Catalog. Other catalogs are listed below
- M: Messier
- ESO: European Southern Observatory
- IRAS: Infrared Astronomical Satellite
- Mrk: Markarian
- UGC: Uppsala General Catalog
Numbers always follow the letters, such as NGC 3314. These numbers indicate the location of the galaxy in the sky, or when the galaxy was entered into the catalog. Also, galaxies can be entered into more than one catalog, so they can have more than one name.
Galactic Morphology
Image courtesy of NASA
An artist's depiction of the collision of the
Andromeda Galaxy and the Milky Way Galaxy
Astronomers know that galaxies are moving in space. Some galaxies are shifting away from the Milky Way, while others are moving towards the Milky Way Galaxy. With all of this shifting, collisions are bound to take place. The interaction of two galaxies is termed galactic cannibalism. Generally, when this happens, the two galaxies merge together to form a larger irregular-shaped galaxy. Will the Milky Way Galaxy ever collide with its neighbors? Astronomers think the answer is "yes." The larger Andromeda Galaxy and the Milky Way may collide in several billion years. Both galaxies are spiral in shape and the resulting collision may create an elliptical galaxy.