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Rosette Nebula (NGC 2237)
emission nebula in Monoceros
The Rosette Nebula is a ring of glowing hydrogen around a young cluster, NGC 2244, in Monoceros. It is large, about 80 arcminutes across (more than two Moon widths), and mostly red, so it responds well to hydrogen-alpha. It is an ideal winter target for mid-focal-length setups.
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// Key facts
- Catalog
- NGC 2237
- Type
- emission nebula
- Constellation
- Monoceros
- Size
- 1.3° across
- Brightness
- Magnitude 9
- Distance
- about 5,000 light-years
- Peak month (any location)
- Dec
- Typical prime months
- Oct to Mar
- Difficulty
- Intermediate
- Filter
- Narrowband: Ha / OIII / SII, or a dual-band / UHC filter
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How to image Rosette Nebula
- A focal length of 300 to 600 mm frames the whole ring.
- Ha and OIII mapped to red and teal give the usual pictorial look.
- The surface is smooth and faint, so flat frames matter, because gradients show easily.
Framing: what focal length?
The focal length at which NGC 2237 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 340 mm |
| APS-C (23.5 mm) | about 610 mm |
| Full frame (36 mm) | about 930 mm |
How high does it climb from your latitude?
The highest point NGC 2237 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) | 40° | Workable |
| 45°N (Minneapolis, Milan) | 50° | Workable |
| 35°N (Los Angeles, Tokyo) | 60° | High in the sky |
| 25°N (Miami, Cairo) | 70° | High in the sky |
| 35°S (Sydney, Santiago) | 50° | Workable |
Also worth imaging
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