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M70
globular cluster in Sagittarius
M70 is a small, compact globular cluster in Sagittarius, the companion of M69 about three degrees away. Together they make a nice pair in a wide field, but both sit low for northern observers.
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// Key facts
- Catalog
- M70
- Type
- globular cluster
- Constellation
- Sagittarius
- Size
- 8′ across
- Brightness
- Magnitude 7.9
- Distance
- about 29,300 light-years
- Peak month (any location)
- Jul
- Typical prime months
- Apr to Sep
- Difficulty
- Advanced
- Filter
- No filter (broadband)
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How to image M70
- Shoot M69 and M70 together in a frame of about 3.5 degrees, or each separately at 1,200 mm or more.
- Dec -32 places it low from the northern United States, so southern observers do much better.
- Short exposures keep the dense core resolved.
Framing: what focal length?
M70 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 10% |
| 2,000 mm | about 20% |
| 3,000 mm | about 30% |
How high does it climb from your latitude?
The highest point M70 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) | 3° | Stays low |
| 45°N (Minneapolis, Milan) | 13° | Stays low |
| 35°N (Los Angeles, Tokyo) | 23° | Stays low |
| 25°N (Miami, Cairo) | 33° | Workable |
| 35°S (Sydney, Santiago) | 87° | High in the sky |
Also worth imaging
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