A Globular Cluster is a sphere shaped grouping of stars. Gravity works to keep the stars close creating a dense center and it also maintains the sphere shape. Currently there are over 150 known globular clusters making them fairly common in our Milky Way and larger galaxies have been found to have 500 or more globular clusters. The stars inside the cluster range in color from blue to red. The red stars are the cooler stars and the blue are the hottest. Stars begin blue in color and burn their hydrogen fuel quickly. Once the hydrogen is burned up, the stars burn helium and begin to change color to a shade closer to red on the color spectrum. In young clusters you will notice more young blue stars and in older clusters you will find more red and white stars.
This particular cluster is Messier 15 or M15 for short. It was discovered by Jean-Dominique Maraldi in 1746 and was included in Messier’s catalogue of comet-like objects. M15 is estimated to be 12 billion years old making it one of the oldest known globular clusters. It is approximately 33,600 light years away from earth and has a luminosity that is 360,000 times brighter than the sun. It is one of the most densely packed clusters in the Milky Way and can be viewed with regular binoculars on a clear night. The cluster has an angular size of 18.0 arc minutes in this image, which corresponds to a linear size of 2.93 light years.In this picture we can see the stars appear to be yellow, orange, and white in color. We also can see the density increase as we are not able to make out individual stars in the center of the cluster.
Kronberg, Christine. "Messier 15." The Messier Catalogue. <http://messier.seds.org/m/m015.html>.
"Messier 15." Wikipedia. <http://en.wikipedia.org/wiki/Messier_15>
"Globular Cluster." Wikipedia. <http://en.wikipedia.org/wiki/Globular_cluster>
|Right Ascension (J2000)||21 29 58.00|
|Declination (J2000)||+12 10 03.0|
|Filters used||B (Blue), R (Red), V (Green)|
|Exposure time per filter||B, V, and R, 60 seconds|
|Date observed||October 19, 2012|