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M68
globular cluster in Hydra
M68 is a modest globular cluster in Hydra, far south in the spring sky. It is less showy than the great globulars but lies in a lonely part of the sky with few bright stars around.
Save your telescope or lens on the planner to lay your camera frame over this diagram.
// Key facts
- Catalog
- M68
- Type
- globular cluster
- Constellation
- Hydra
- Size
- 12′ across
- Brightness
- Magnitude 7.8
- Distance
- about 33,600 light-years
- Peak month (any location)
- Mar
- Typical prime months
- Jan to Jun
- Difficulty
- Intermediate
- Filter
- No filter (broadband)
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How to image M68
- Only 12 arcminutes across, so 1,000 mm or more suits it.
- Dec -27 puts it low from the northern United States, so plan for the meridian crossing in spring.
- The sparse surroundings make it a clean target for deep stacks.
Framing: what focal length?
M68 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 15% |
| 2,000 mm | about 30% |
| 3,000 mm | about 45% |
How high does it climb from your latitude?
The highest point M68 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) | 8° | Stays low |
| 45°N (Minneapolis, Milan) | 18° | Stays low |
| 35°N (Los Angeles, Tokyo) | 28° | Stays low |
| 25°N (Miami, Cairo) | 38° | Workable |
| 35°S (Sydney, Santiago) | 82° | High in the sky |
Also worth imaging
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