M3 · Messier 3
| Chinese name | 猎犬座球状星团 |
|---|---|
| Type | Globular cluster |
| Constellation | CVn |
| RA | 13h42m |
| Dec | +28° |
| Apparent magnitude | 6.2ᵐ |
| Hemisphere | Northern |
| Best season | Spring |
| Difficulty | Moderate |
| Focal length | 长焦 1000mm+ |
About
M3 lies about 34,000 light-years away in Canes Venatici and is one of the brightest, richest globular clusters in the sky, containing roughly 500,000 stars. It is famous for its hundreds of RR Lyrae variables (about 274 confirmed), among the most of any globular, standard candles vital for measuring cosmic distances. Around 11.5 billion years old, it is symmetric with a densely concentrated, bright core whose stars thin out toward the edges. At magnitude 6.2 it shows as a fuzzy patch in binoculars, while medium telescopes resolve its outer stars. It is a popular long-focus globular of the spring sky, rewarding high-resolution imaging.