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M100
spiral galaxy in Coma Berenices
M100 is a large, face-on grand-design spiral in Coma Berenices, with two prominent arms and many smaller ones. It was one of the first galaxies where the Hubble Space Telescope measured Cepheid variable stars to calibrate distances.
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// Key facts
- Catalog
- M100
- Type
- spiral galaxy
- Constellation
- Coma Berenices
- Size
- 7′ across
- Brightness
- Magnitude 9.3
- Distance
- about 55 million light-years
- Peak month (any location)
- Mar
- Typical prime months
- Jan to Jun
- Difficulty
- Intermediate
- Filter
- No filter (broadband); a light-pollution filter is optional
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 M100
- At 7 arcminutes, use 1,200 to 2,000 mm.
- Dark skies and long exposure bring out the faint outer arms.
- Best in spring evenings from northern sites.
Framing: what focal length?
M100 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 9% |
| 2,000 mm | about 17% |
| 3,000 mm | about 26% |
How high does it climb from your latitude?
The highest point M100 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) | 51° | Workable |
| 45°N (Minneapolis, Milan) | 61° | High in the sky |
| 35°N (Los Angeles, Tokyo) | 71° | High in the sky |
| 25°N (Miami, Cairo) | 81° | High in the sky |
| 35°S (Sydney, Santiago) | 39° | Workable |
Also worth imaging
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