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Butterfly Cluster (M6)
open cluster in Scorpius
The Butterfly Cluster is a bright open cluster in Scorpius, named for the wing-like pattern of its stars. It sits in a rich part of the Milky Way near the tail of the scorpion, only a few degrees from M7.
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// Key facts
- Catalog
- M6
- Type
- open cluster
- Constellation
- Scorpius
- Size
- 25′ across
- Brightness
- Magnitude 4.2
- Distance
- about 1,600 light-years
- Peak month (any location)
- Jun
- Typical prime months
- Apr to Aug
- Difficulty
- Intermediate
- Filter
- No filter (broadband)
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How to image Butterfly Cluster
- M6 and M7 are about four degrees apart. A wide frame of 5 degrees or more (roughly 200 mm on APS-C) can show both.
- It is far south (dec -32), so it is low from northern sites. Southern hemisphere imagers have the best views.
- Broadband only. Watch the brighter stars for blooming and halos.
Framing: what focal length?
The focal length at which M6 spans about 60% of the long side of the sensor, leaving room around it. Treat it as a starting point; the right framing is a matter of taste.
| Sensor | Focal length |
|---|---|
| 1-inch sensor (13.2 mm) | about 1090 mm |
| APS-C (23.5 mm) | about 1940 mm |
| Full frame (36 mm) | about 2970 mm |
How high does it climb from your latitude?
The highest point M6 reaches in the sky. Above about 60° is excellent, 30° to 60° is workable, and under 30° you are looking through a lot of air.
| Latitude | Highest point | Rating |
|---|---|---|
| 55°N (Scotland, Alaska) | 3° | Stays low |
| 45°N (Minneapolis, Milan) | 13° | Stays low |
| 35°N (Los Angeles, Tokyo) | 23° | Stays low |
| 25°N (Miami, Cairo) | 33° | Workable |
| 35°S (Sydney, Santiago) | 87° | High in the sky |
Also worth imaging
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