M6 · Butterfly Cluster
| Chinese name | 蝴蝶星团 |
|---|---|
| Type | Open cluster |
| Constellation | Sco |
| RA | 17h40m |
| Dec | −32° |
| Apparent magnitude | 4.2ᵐ |
| Hemisphere | Southern |
| Best season | Summer |
| Difficulty | Easy |
| Focal length | 中焦 400–800mm |
About
The Butterfly Cluster (M6, NGC 6405) lies about 1,600 light-years away in the tail of Scorpius, named for bright member stars arranged like a butterfly with open wings. It contains about eighty brighter stars, mostly hot blue-white B-type stars, while its brightest member, BM Scorpii, is an orange semiregular variable that stands out vividly amid the blue-white throng. Around 100 million years old, the cluster is set against the densest, richest star fields of the Scorpius Milky Way and is visible to the naked eye. It is an easy, bright open cluster to image in the southern summer sky, well suited to medium focal lengths that bring out the glittering stars and wing shape.