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Hercules Cluster (M13)
globular cluster in Hercules
The Great Globular Cluster in Hercules is the showpiece globular of the northern sky: a dense ball of several hundred thousand stars packed into about twenty arcminutes. It shines in broadband light, so it is an easy target under moderate light pollution, and a small galaxy, NGC 6207, shares the field.
Save your telescope or lens on the planner to lay your camera frame over this diagram.
// Key facts
- Catalog
- M13
- Type
- globular cluster
- Constellation
- Hercules
- Size
- 20′ across
- Brightness
- Magnitude 5.8
- Distance
- about 22,000 light-years
- Peak month (any location)
- May
- Typical prime months
- Mar to Aug
- 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 Hercules Cluster
- Use a focal length of about 800 mm or more, otherwise the cluster is a small ball in a large frame.
- Short subs keep the core from saturating. The center resolves into individual stars only if it is not blown out.
- No filter is needed. Spend your time on focus and tracking, since a globular punishes soft stars.
Framing: what focal length?
The focal length at which M13 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 1360 mm |
| APS-C (23.5 mm) | about 2420 mm |
| Full frame (36 mm) | about 3710 mm |
How high does it climb from your latitude?
The highest point M13 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) | 71° | High in the sky |
| 45°N (Minneapolis, Milan) | 81° | High in the sky |
| 35°N (Los Angeles, Tokyo) | 89° | High in the sky |
| 25°N (Miami, Cairo) | 79° | High in the sky |
| 35°S (Sydney, Santiago) | 19° | Stays low |
Also worth imaging
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