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M54
globular cluster in Sagittarius
M54 looks like an ordinary globular cluster in Sagittarius, but it is not part of the Milky Way. It sits in the core of the Sagittarius Dwarf Galaxy, a small galaxy being pulled apart by the Milky Way, which makes it one of the more distant globulars in the Messier list.
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// Key facts
- Catalog
- M54
- Type
- globular cluster
- Constellation
- Sagittarius
- Size
- 12′ across
- Brightness
- Magnitude 7.6
- Distance
- about 87,000 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 M54
- It is compact, only 12 arcminutes, so use 1,000 mm or more.
- At its distance the stars are faint, so a longer total exposure is needed.
- It is far south (dec -30), so choose a clear southern horizon, and expect it to be low from the northern United States.
Framing: what focal length?
M54 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 M54 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) | 5° | Stays low |
| 45°N (Minneapolis, Milan) | 15° | Stays low |
| 35°N (Los Angeles, Tokyo) | 25° | Stays low |
| 25°N (Miami, Cairo) | 35° | Workable |
| 35°S (Sydney, Santiago) | 85° | High in the sky |
Also worth imaging
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