M15

From South Dublin Astronomical Society

M15
Type	Globular cluster
NGC	NGC 7078
Constellation	Pegasus
Right Ascension	21h 30m
Declination	+12° 10’
Magnitude	6.4
Size	12 arc min.
Image:M15 messier image.jpg

M15 is a bright globular that rivals the better known M13 in Hercules. The cluster appears as a fluffy 6th magnitude spot of light in binoculars set within a field of three relatively bright stars forming an isoceles triangle. Make a note of which one M15 appears closest to in your sketch of the scene. To find this delightful object you just need to wing your way less than four degrees northwest of magnitude 2·4 Epsilion Pegasi, or Enif (itself a binocular double with an 8·4m companion 143 arc-seconds distant.) Lower power binoculars will let you fit Enif and the cluster in the same field. The cluster is 33,600 light years distant and about 175 light years across. It was also the first shown to harbour a planetary nebulae, Pease 1, recorded on photographic plates taken in 1927. There are strong hints too that a black hole resides at the core. Half the mass of M15 is packed into a sphere 10 light years across so close encounters between stars there must be common.