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Great Sagittarius Cluster (M22)
globular cluster in Sagittarius
M22 is among the brightest and nearest of the large globular clusters, and in many ways rivals M13. It is a rich ball of resolved stars in Sagittarius, though it sits so far south that northern observers see it low in the sky.
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// Key facts
- Catalog
- M22
- Type
- globular cluster
- Constellation
- Sagittarius
- Size
- 32′ across
- Brightness
- Magnitude 5.1
- Distance
- about 10,400 light-years
- Peak month (any location)
- Jun
- Typical prime months
- Apr to Sep
- Difficulty
- Intermediate
- Filter
- No filter (broadband)
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How to image Great Sagittarius Cluster
- It is far south (dec -24), so from northern latitudes it never climbs high. Southern hemisphere and low-latitude sites see it much better.
- At 32 arcminutes it fits well in 600 to 1,000 mm, with plenty of space for the halo.
- M28 lies about three degrees away and can fit in a wider frame, along with the Lagoon Nebula region farther north.
Framing: what focal length?
The focal length at which M22 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 850 mm |
| APS-C (23.5 mm) | about 1510 mm |
| Full frame (36 mm) | about 2320 mm |
How high does it climb from your latitude?
The highest point M22 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) | 11° | Stays low |
| 45°N (Minneapolis, Milan) | 21° | Stays low |
| 35°N (Los Angeles, Tokyo) | 31° | Workable |
| 25°N (Miami, Cairo) | 41° | Workable |
| 35°S (Sydney, Santiago) | 79° | High in the sky |
Also worth imaging
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