Go / no go for deep skyGo / no go for deep sky imaging
Thor's Helmet (NGC 2359)
emission nebula in Canis Major
Thor's Helmet is an emission nebula in Canis Major shaped like a winged helmet, created by the strong wind of a Wolf-Rayet star at its center. It is bright in Ha and OIII, and the thin filaments of the helmet's wings look especially good with narrowband.
Save your telescope or lens on the planner to lay your camera frame over this diagram.
// Key facts
- Catalog
- NGC 2359
- Type
- emission nebula
- Constellation
- Canis Major
- Size
- 8′ across
- Brightness
- Magnitude 11.5
- Distance
- roughly 12,000 to 15,000 light-years
- Peak month (any location)
- Jan
- Typical prime months
- Oct to Mar
- Difficulty
- Intermediate
- Filter
- Narrowband: Ha / OIII / SII, or a dual-band / UHC filter
Pick a saved location or share your device location. Your coordinates are used only to calculate tonight and are not stored. To save locations, use the planner.
How to image Thor's Helmet
- Ha and OIII bring out the wings, which are faint in broadband.
- At 8 arcminutes for the helmet itself (with larger faint wings), use 800 to 1,200 mm.
- Dec -13 is moderate in altitude from northern sites in winter.
Framing: what focal length?
NGC 2359 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 10% |
| 2,000 mm | about 20% |
| 3,000 mm | about 30% |
How high does it climb from your latitude?
The highest point NGC 2359 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) | 22° | Stays low |
| 45°N (Minneapolis, Milan) | 32° | Workable |
| 35°N (Los Angeles, Tokyo) | 42° | Workable |
| 25°N (Miami, Cairo) | 52° | Workable |
| 35°S (Sydney, Santiago) | 68° | High in the sky |
Also worth imaging
Want a GO / NO-GO verdict for tonight, with clouds, moon, seeing and a full dark-window timeline?
Open the planner