Messier 15, a Globular Cluster located in the constellation Pegasus was discovered in 1746 by Jean-Dominique Maraldi. A globular cluster is a large collection of stars arranged in a sphere and orbits a galactic core. The strong gravitational pull of the cluster towards the center gives it a nice spherical shape. Globular clusters are always found in the halo of a galaxy, an extended spherical component of a galaxy which extends out of our point of view. There are roughly 150 known globular clusters and nearly every galaxy has an associated group of globular clusters. Globular clusters contain many more stars and are packed more tightly together than open clusters.
Above is an image of globular cluster M15 = NGC 7078. You can see there are many stars packed tightly together in a spherical shape which is characteristic of globular clusters. There is a clear contrast between the many stars tightly bunched in the cluster when compared to the vast openness that surrounds it which the picture clearly illustrates. Within the cluster you can see the center is more dense than its surrounding and as a result is brighter and creates the spherical shape. M 15 lies about 33,500 light years away from earth with a linear size of 100 x 130 light years.
Frommert, Hartmut, and Christine Kronberg. "Messier 15."Students for the Exploration and Development of Space. Web 8 Nov. 2012<http://www.seds.org/messier//m/m015.html>.
Frommert, Hartmut, and Christine Kronberg. "Autumn." The RASC's Finest N.G.C Objects List. 6 Jan. 2005. Web. 8 Nov. 2012. <http://www.seds.org/messier/xtra/similar/rasc-ngc.html>.
|Right Ascension (J2000)||21:29':58"|
|Filters used||B (Blue), R (Red), V (Green)|
|Exposure time per filter||B, V, and R (6s)|
|Date observed||October 20, 2012|