Globular clusters can be identified by two observable criteria: the spherical collection of stars and the dense center that the star cluster orbits. Their spherical shape is due to the intense amount of gravity which increases towards the center of the cluster. Globular clusters have significantly older and higher number of stars compared to galactic or open clusters. These clusters are fairly common--there are over 150 globular clusters in the Milky Way.
Messier 2 (also known as NGC 7089) is a globular cluster in the constellation Aquarius discovered by Jean-Dominique Maraldi in 1746. Its radius is 87.3 light years making this cluster is one of the largest known globular clusters (Wikipedia). For being around 37,000 light years from earth, Messier 2 is visible to the naked eye under extremely good conditions.
Messier 2 contains about 150,000 stars and is one of the oldest star clusters in the Milky Way. Its brightest stars are red and yellow giants. The color of the stars suggests the relative age of the stars. Blue stars are much hotter and younger; when these stars burn out, they become the red stars which are cooler in temperature and more massive. These red stars last a very long time, almost indefinitely.
|Right Ascension (J2000)||21 33 27.20|
|Declination (J2000)||-00 49 22.0|
|Filters used||B (Blue), R (Red), V (Green)|
|Exposure time per filter||B, V, and R (300s); C (60s x 5)|
|Date and Time observed||October 19, 2012; 11:24:44 (EST)|