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Omega Centauri (NGC 5139)
globular cluster in Centaurus
Omega Centauri is the largest and most massive globular cluster in the Milky Way, with several million stars. It is so big that it may be the remaining core of a small galaxy that was torn apart long ago. It is bright enough to see with the naked eye from the southern hemisphere.
Save your telescope or lens on the planner to lay your camera frame over this diagram.
// Key facts
- Catalog
- NGC 5139
- Type
- globular cluster
- Constellation
- Centaurus
- Size
- 36′ across
- Brightness
- Magnitude 3.9
- Distance
- about 17,000 light-years
- Peak month (any location)
- Apr
- Typical prime months
- Jan to Jun
- Difficulty
- Intermediate
- Filter
- No filter (broadband)
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How to image Omega Centauri
- It is deep south (dec -47), so it only climbs high for southern hemisphere and low-latitude sites. From the northern United States it stays near the horizon.
- At 36 arcminutes it fills a frame at 500 to 800 mm, with the halo visible.
- The dense core clips easily, so blend in short exposures to keep it resolved.
Framing: what focal length?
The focal length at which NGC 5139 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 760 mm |
| APS-C (23.5 mm) | about 1350 mm |
| Full frame (36 mm) | about 2060 mm |
How high does it climb from your latitude?
The highest point NGC 5139 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) | below horizon | Never rises |
| 45°N (Minneapolis, Milan) | below horizon | Never rises |
| 35°N (Los Angeles, Tokyo) | 8° | Stays low |
| 25°N (Miami, Cairo) | 18° | Stays low |
| 35°S (Sydney, Santiago) | 78° | High in the sky |
Also worth imaging
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