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Cocoon Nebula (IC 5146)
emission nebula in Cygnus
The Cocoon Nebula is a small, round blend of emission and reflection nebula in Cygnus, at the head of a long dark dust lane called Barnard 168. A young cluster is embedded within it.
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// Key facts
- Catalog
- IC 5146
- Type
- emission nebula
- Constellation
- Cygnus
- Size
- 12′ across
- Brightness
- Magnitude 7.2
- Distance
- about 3,300 to 4,000 light-years
- Peak month (any location)
- Aug
- Typical prime months
- Jun to Nov
- Difficulty
- Intermediate
- Filter
- Narrowband: Ha / OIII / SII, or a dual-band / UHC filter
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How to image Cocoon Nebula
- At 12 arcminutes, use 1,000 to 1,500 mm for a close-up, or a wider frame to include the dark lane.
- Ha or dual-band for the emission, while the reflection needs broadband.
- Cygnus is high in the summer and autumn sky.
Framing: what focal length?
IC 5146 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 IC 5146 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) | 82° | High in the sky |
| 45°N (Minneapolis, Milan) | 88° | High in the sky |
| 35°N (Los Angeles, Tokyo) | 78° | High in the sky |
| 25°N (Miami, Cairo) | 68° | High in the sky |
| 35°S (Sydney, Santiago) | 8° | Stays low |
Also worth imaging
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