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Coma Pinwheel Galaxy (M99)
spiral galaxy in Coma Berenices
M99, the Coma Pinwheel, is a face-on spiral galaxy with noticeably lopsided arms, probably distorted by a past encounter with another galaxy. It is in the northern part of the Virgo Cluster.
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// Key facts
- Catalog
- M99
- Type
- spiral galaxy
- Constellation
- Coma Berenices
- Size
- 5′ across
- Brightness
- Magnitude 9.9
- Distance
- about 50 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
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How to image Coma Pinwheel Galaxy
- At 5 arcminutes, use 1,500 mm or more.
- M100 is about 1.5 degrees away, so a mid-width frame can include both.
- Best in spring evenings from northern sites.
Framing: what focal length?
M99 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 6% |
| 2,000 mm | about 12% |
| 3,000 mm | about 19% |
How high does it climb from your latitude?
The highest point M99 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) | 49° | Workable |
| 45°N (Minneapolis, Milan) | 59° | Workable |
| 35°N (Los Angeles, Tokyo) | 69° | High in the sky |
| 25°N (Miami, Cairo) | 79° | High in the sky |
| 35°S (Sydney, Santiago) | 41° | Workable |
Also worth imaging
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