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M23
open cluster in Sagittarius
M23 is a large, rich open cluster in Sagittarius with a few hundred stars. It sits in a rich star field between the Lagoon region and the Scutum star clouds, and it is a good wide-field subject.
Save your telescope or lens on the planner to lay your camera frame over this diagram.
// Key facts
- Catalog
- M23
- Type
- open cluster
- Constellation
- Sagittarius
- Size
- 27′ across
- Brightness
- Magnitude 6.9
- Distance
- about 2,150 light-years
- Peak month (any location)
- Jun
- Typical prime months
- Apr to Sep
- Difficulty
- Beginner
- Filter
- No filter (broadband)
Pick a saved location or share your device location. Your coordinates are used only to calculate tonight and are not stored. To save locations, use the planner.
How to image M23
- At 27 arcminutes, 400 to 800 mm frames it well.
- A rich star field makes guiding quality obvious, so check star shapes carefully.
- Dec -19 is low from northern sites.
Framing: what focal length?
The focal length at which M23 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 1010 mm |
| APS-C (23.5 mm) | about 1800 mm |
| Full frame (36 mm) | about 2750 mm |
How high does it climb from your latitude?
The highest point M23 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) | 16° | Stays low |
| 45°N (Minneapolis, Milan) | 26° | Stays low |
| 35°N (Los Angeles, Tokyo) | 36° | Workable |
| 25°N (Miami, Cairo) | 46° | Workable |
| 35°S (Sydney, Santiago) | 74° | High in the sky |
Also worth imaging
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