Go / no go for deep skyGo / no go for deep sky imaging
Pinwheel Galaxy (M101)
spiral galaxy in Ursa Major
The Pinwheel Galaxy is a big, face-on spiral in Ursa Major, nearly as wide as the Moon. Its light is spread so thinly that it is one of the hardest big galaxies to photograph: it looks like a faint smudge in a short exposure and only reveals its arms under dark skies and long integration. It hosted a bright supernova in 2023.
Save your telescope or lens on the planner to lay your camera frame over this diagram.
// Key facts
- Catalog
- M101
- Type
- spiral galaxy
- Constellation
- Ursa Major
- Size
- 29′ across
- Brightness
- Magnitude 7.9
- Distance
- about 21 million light-years
- Peak month (any location)
- Apr
- Typical prime months
- Feb to Jul
- Difficulty
- Advanced
- Filter
- No filter (broadband); a light-pollution filter is optional
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How to image Pinwheel Galaxy
- This galaxy rewards dark skies more than almost any other target. Under suburban light pollution, expect a faint result.
- Plan for many hours of total exposure and a moonless window.
- A focal length of 800 to 1,600 mm fills an APS-C frame comfortably; shorter works if you want space around it.
Framing: what focal length?
The focal length at which M101 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 940 mm |
| APS-C (23.5 mm) | about 1670 mm |
| Full frame (36 mm) | about 2560 mm |
How high does it climb from your latitude?
The highest point M101 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) | 89° | High in the sky |
| 45°N (Minneapolis, Milan) | 81° | High in the sky |
| 35°N (Los Angeles, Tokyo) | 71° | High in the sky |
| 25°N (Miami, Cairo) | 61° | High in the sky |
| 35°S (Sydney, Santiago) | 1° | Stays low |
Also worth imaging
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