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Physics & Astronomy Department

Astr111 Photography Projects, Fall 2009

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Pegasus II Cluster , Lea Boehlke

Helix Nebula

To begin with, galaxies are large systems of stars and interstellar material. Galaxies can consist of several million to several trillion stars with a range of masses several million to several trillion times that of our own sun. Galaxies also vary in design; they are put into different groups such as spiral, lenticular, elliptical and irregular. Throughout the universe galaxies generally form in groups or clusters. These groups can range from a few or a few dozen or up to several thousand galaxies. Within a cluster, the galaxies are in mutual gravitational interaction and are probably the largest structures in the universe where a self-gravitational system has been formed. Galaxy clusters are classified into two sections known as regular and irregular clusters. Regular clusters have a concentrated central core, a well defined spherical structure and consist of galaxies ranging in the same size. Irregular clusters don't have a well-defined center, but do have a similar size range of galaxies. The Pegasus II Cluster is a cluster of galaxies found in the constellation of Pegasus (The Winged Horse). This cluster is thought to be about 550 million light years away.

This image is a mosaic made up of four smaller pictures. If this cluster were bright enough to see on Earth without a telescope it would seem to be about the size of the moon. This image shows numerous galaxies within the Pegasus II Cluster. The galaxies appear as a bright core with a fuzzy outline. At least 14 different galaxies are able to be seen in this image. One easily visible spiral galaxy is located in the middle near the top of the picture. It has a bright core with a spiral fuzzy disk around it. Another galaxy that can be spotted is an elliptical galaxy that can be found on the left side almost near the bottom. This type of galaxy has an ellipsoidal shape. One galaxy that may not be as easy to locate or recognize would be the lenticular galaxy at the top middle of the image above the previously talked about spiral galaxy. This type of galaxy is basically a spiral galaxy without the spiral structure. To see a larger version of the image click here. The linear size of this cluster is about 2.3 million light years across.

References:

Brewster, Jon. "Pegasus II Cluster." Jon's Astronomy Pages.
<http://www.proaxis.com/~sandstone/Astro/Gallery/N7720.htm>.

Frommert, Hartmut and Kronberg, Christine. "Galaxies." Students for the Exploration and Development of Space.
<http://seds.lpl.arizona.edu/MESSIER/galaxy.html>.

Frommert, Hartmut and Kronberg, Christine. "Groups and Clusters of Galaxies." Students for the Exploration and Development of Space.
<http://seds.org/messier/gal_clus.html>.

"Galaxy Clusters and Large-scale Structure." Cambridge Cosmology: Galaxies.
<http://www.damtp.cam.ac.uk/research/gr/public/gal_lss.html>.

Huchra,John, Chen,Jacqueline, McNamara, Brian and Mader, Jeff . "Redshifts in Nearby Rich Clusters of Galaxies."
<http://www.cfa.harvard.edu/~huchra/clusters/>.

J. Rick. "Pegasus II Galaxy Cluster." Cloudy Night Telescope Reviews.
<http://www.cloudynights.com/ubbthreads/showthreaded.php/Cat/0/Number/2837921/page/0/view/collapsed/sb/5/o/all>.

Right Ascension (J2000) 23:38:28.5
Declination (J2000) 27:01:52
Filters used clear(C)
Exposure time per filter 300 seconds in C
Date observed

November 8, 2009 (C)