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Crescent Nebula (NGC 6888)
emission nebula in Cygnus
The Crescent Nebula is a shell of glowing gas in Cygnus, blown out by the fierce wind of a Wolf-Rayet star. Its thin arcs and filaments are rich in oxygen, and the bright shell is surrounded by much fainter material.
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// Key facts
- Catalog
- NGC 6888
- Type
- emission nebula
- Constellation
- Cygnus
- Size
- 20′ across
- Brightness
- Magnitude 7.4
- Distance
- about 5,000 light-years
- Peak month (any location)
- Jul
- Typical prime months
- May to Oct
- Difficulty
- Intermediate
- Filter
- Narrowband: Ha / OIII / SII, or a dual-band / UHC filter
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How to image Crescent Nebula
- OIII and Ha capture the shell. OIII is particularly important for the fainter outer loops.
- At 20 arcminutes, use 600 to 1,000 mm.
- Cygnus is high in the summer sky from northern latitudes.
Framing: what focal length?
The focal length at which NGC 6888 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 1360 mm |
| APS-C (23.5 mm) | about 2420 mm |
| Full frame (36 mm) | about 3710 mm |
How high does it climb from your latitude?
The highest point NGC 6888 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) | 73° | High in the sky |
| 45°N (Minneapolis, Milan) | 83° | High in the sky |
| 35°N (Los Angeles, Tokyo) | 87° | High in the sky |
| 25°N (Miami, Cairo) | 77° | High in the sky |
| 35°S (Sydney, Santiago) | 17° | Stays low |
Also worth imaging
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