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Skull Nebula (NGC 246)
planetary nebula in Cetus
The Skull Nebula is a faint planetary nebula in Cetus, shaped like a skull because of dark gaps in the ring. It has a bright central star and a few fainter field stars close to the nebula. It is a challenging, low-contrast target.
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// Key facts
- Catalog
- NGC 246
- Also known as
- C 56, Caldwell 56
- Type
- planetary nebula
- Constellation
- Cetus
- Size
- 4′ across
- Brightness
- Magnitude 10.9
- Distance
- roughly 1,600 to 2,000 light-years
- Peak month (any location)
- Oct
- Typical prime months
- Jul to Dec
- Difficulty
- Advanced
- Filter
- OIII or dual-band / UHC filter
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How to image Skull Nebula
- It is about 4 arcminutes across; use 1,000 to 1,500 mm.
- An OIII or dual-band filter, plus a dark sky, helps the faint ring show.
- Cetus is well placed in autumn evenings from the northern hemisphere.
Framing: what focal length?
NGC 246 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 5% |
| 2,000 mm | about 10% |
| 3,000 mm | about 15% |
How high does it climb from your latitude?
The highest point NGC 246 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) | 23° | Stays low |
| 45°N (Minneapolis, Milan) | 33° | Workable |
| 35°N (Los Angeles, Tokyo) | 43° | Workable |
| 25°N (Miami, Cairo) | 53° | Workable |
| 35°S (Sydney, Santiago) | 67° | High in the sky |
Also worth imaging
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