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M3
globular cluster in Canes Venatici
M3 is often named among the finest globular clusters in the northern sky. It holds around half a million stars and is unusually rich in variable stars. It sits in Canes Venatici, away from the Milky Way, so the background is clean and dark.
Save your telescope or lens on the planner to lay your camera frame over this diagram.
// Key facts
- Catalog
- M3
- Type
- globular cluster
- Constellation
- Canes Venatici
- Size
- 18′ across
- Brightness
- Magnitude 6.2
- Distance
- about 34,000 light-years
- Peak month (any location)
- Apr
- Typical prime months
- Jan to Jun
- Difficulty
- Beginner
- Filter
- No filter (broadband)
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How to image M3
- Spring evenings suit it well, and it stays high from mid-northern latitudes, which helps resolve the fine stars.
- The packed core burns out easily. Short exposures blended into the main stack keep the individual stars separated.
- A focal length of 800 to 1,200 mm frames it with room for the halo, and good guiding makes the faint outer stars crisper.
Framing: what focal length?
M3 is small, so a "60% of the frame" focal length would be impractical. Here is how much of an APS-C frame it covers at common long focal lengths; expect to crop.
| Focal length | Share of the frame width |
|---|---|
| 1,000 mm | about 22% |
| 2,000 mm | about 45% |
| 3,000 mm | about 67% |
How high does it climb from your latitude?
The highest point M3 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) | 63° | High in the sky |
| 45°N (Minneapolis, Milan) | 73° | High in the sky |
| 35°N (Los Angeles, Tokyo) | 83° | High in the sky |
| 25°N (Miami, Cairo) | 87° | High in the sky |
| 35°S (Sydney, Santiago) | 27° | Stays low |
Also worth imaging
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