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Question Mark Nebula (NGC 7822)
emission nebula in Cepheus
The Question Mark Nebula is a large, faint emission nebula in Cepheus, with bright pillars and a curve that gives it its name. It is part of a large star-forming region, and it rewards narrowband imaging.
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// Key facts
- Catalog
- NGC 7822
- Type
- emission nebula
- Constellation
- Cepheus
- Size
- 1.0° across
- Brightness
- Magnitude 8
- Distance
- about 3,000 light-years
- Peak month (any location)
- Sep
- Typical prime months
- Jul to Dec
- Difficulty
- Advanced
- Filter
- Narrowband: Ha / OIII / SII, or a dual-band / UHC filter
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How to image Question Mark Nebula
- Ha, OIII and SII narrowband give the best results. It is faint in broadband.
- At 60 arcminutes, use 300 to 600 mm.
- It is far north (dec +68) so it is circumpolar from much of the northern hemisphere.
Framing: what focal length?
The focal length at which NGC 7822 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 450 mm |
| APS-C (23.5 mm) | about 810 mm |
| Full frame (36 mm) | about 1240 mm |
How high does it climb from your latitude?
The highest point NGC 7822 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) | 76° | High in the sky |
| 45°N (Minneapolis, Milan) | 66° | High in the sky |
| 35°N (Los Angeles, Tokyo) | 56° | Workable |
| 25°N (Miami, Cairo) | 46° | Workable |
| 35°S (Sydney, Santiago) | below horizon | Never rises |
Also worth imaging
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