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Helix Nebula (NGC 7293)
planetary nebula in Aquarius
The Helix Nebula is one of the nearest planetary nebulae to Earth, which makes it large, about 25 arcminutes (nearly the width of the full Moon), and also very faint, since its light is spread thin. It lies in Aquarius at a fairly southern declination, so it stays low for observers in the north.
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// Key facts
- Catalog
- NGC 7293
- Type
- planetary nebula
- Constellation
- Aquarius
- Size
- 25′ across
- Brightness
- Magnitude 7.6
- Distance
- about 650 light-years
- Peak month (any location)
- Aug
- Typical prime months
- Jun to Nov
- Difficulty
- Intermediate
- Filter
- OIII or dual-band / UHC filter
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How to image Helix Nebula
- Use 500 to 1,000 mm for a good fill. It rewards long total exposure.
- OIII and Ha reveal the outer rings of gas, which are hardly visible in broadband.
- Southern observers have a big advantage; from far north, wait for the clearest and steadiest nights.
Framing: what focal length?
The focal length at which NGC 7293 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 1090 mm |
| APS-C (23.5 mm) | about 1940 mm |
| Full frame (36 mm) | about 2970 mm |
How high does it climb from your latitude?
The highest point NGC 7293 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) | 14° | Stays low |
| 45°N (Minneapolis, Milan) | 24° | Stays low |
| 35°N (Los Angeles, Tokyo) | 34° | Workable |
| 25°N (Miami, Cairo) | 44° | Workable |
| 35°S (Sydney, Santiago) | 76° | High in the sky |
Also worth imaging
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