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Omega Nebula (M17)
emission nebula in Sagittarius
The Omega Nebula, also called the Swan, is one of the brightest and best-defined emission nebulae in the sky. A bright bar of gas curves into a hook that looks like a swan's neck. Because it is bright, it gives a strong image even in a modest exposure time.
Save your telescope or lens on the planner to lay your camera frame over this diagram.
// Key facts
- Catalog
- M17
- Type
- emission nebula
- Constellation
- Sagittarius
- Size
- 46′ across
- Brightness
- Magnitude 6
- Distance
- about 5,500 light-years
- Peak month (any location)
- Jun
- Typical prime months
- Apr to Sep
- Difficulty
- Intermediate
- Filter
- Narrowband: Ha / OIII / SII, or a dual-band / UHC filter
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How to image Omega Nebula
- A focal length of 600 to 1,000 mm fills the frame with the bright part of the nebula.
- Ha and OIII show the different layers of glowing gas well.
- Wait for the nights when it is highest in the south, since it never climbs far for northern observers.
Framing: what focal length?
The focal length at which M17 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 590 mm |
| APS-C (23.5 mm) | about 1050 mm |
| Full frame (36 mm) | about 1610 mm |
How high does it climb from your latitude?
The highest point M17 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) | 19° | Stays low |
| 45°N (Minneapolis, Milan) | 29° | Stays low |
| 35°N (Los Angeles, Tokyo) | 39° | Workable |
| 25°N (Miami, Cairo) | 49° | Workable |
| 35°S (Sydney, Santiago) | 71° | High in the sky |
Also worth imaging
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