Alt. Designations: NGC 7078
Object Type: Globular  Cluster
Constellation: Pegasus
Distance: 33.6 kly
Right Ascension: 21h 29m 58.3s
Declination: +12° 10´ 03"
Visual Magnitude: 6.4
Apparent Dimension: 18.0´ Dia.
Best Month To View: Aug

Messier 15 or M15 (also designated NGC 7078) is a globular cluster in the constellation Pegasus. At an estimated 12.0 billion years old, it is one of the oldest known globular clusters. M15 is about 33,600 light-years from Earth, and 175 light years in diameter. It has an absolute magnitude of -9.2, which translates to a total luminosity of 360,000 times that of the Sun. Messier 15 is one of the most densely packed globulars known in the Milky Way galaxy. Its core has undergone a contraction known as 'core collapse' and it has a central density cusp with an enormous number of stars surrounding what may be a central black hole. Home to over 100,000 stars, the cluster is notable for containing a large number of variable stars (112) and pulsars (8), including one double neutron star system, M15 C. M15 also contains Pease 1, the first planetary nebula discovered within a globular cluster in 1928. Just three others have been found in globular clusters since then.