M15 · Messier 15
| Chinese name | 飞马座球状星团 |
|---|---|
| Type | Globular cluster |
| Constellation | Peg |
| RA | 21h30m |
| Dec | +12° |
| Apparent magnitude | 6.2ᵐ |
| Hemisphere | Both hemispheres |
| Best season | Autumn |
| Difficulty | Moderate |
| Focal length | 长焦 1000mm+ |
About
M15 (NGC 7078) lies about 33,000 light-years away in Pegasus and is one of the densest-core globular clusters known. Its center has undergone "core collapse," with stellar density spiking sharply toward a tight cusp, and the core may harbor an intermediate-mass black hole. It is also one of the few globulars to contain a planetary nebula: Pease 1, discovered in 1928, was the first planetary nebula confirmed within a globular cluster. About 12 billion years old, M15 contains hundreds of thousands of stars and over a hundred variables. Symmetric and bright, just glimpsed with the naked eye, it is a rewarding autumn target for long-focal globular-cluster imaging.