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M103
open cluster in Cassiopeia
M103 is a small, compact open cluster in Cassiopeia, near the end of the W shape. A few other clusters, such as NGC 654, 659 and 663, lie nearby, so a wide frame of this area is a collection of small open clusters.
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// Key facts
- Catalog
- M103
- Type
- open cluster
- Constellation
- Cassiopeia
- Size
- 6′ across
- Brightness
- Magnitude 7.4
- Distance
- about 8,000 light-years
- Peak month (any location)
- Oct
- Typical prime months
- Jul to Dec
- Difficulty
- Intermediate
- Filter
- No filter (broadband)
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How to image M103
- At 6 arcminutes it is small, so 1,200 mm or more for a close-up.
- A wide frame can capture several clusters in this part of Cassiopeia.
- High in the autumn sky from northern sites.
Framing: what focal length?
M103 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 7% |
| 2,000 mm | about 15% |
| 3,000 mm | about 22% |
How high does it climb from your latitude?
The highest point M103 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) | 84° | High in the sky |
| 45°N (Minneapolis, Milan) | 74° | High in the sky |
| 35°N (Los Angeles, Tokyo) | 64° | High in the sky |
| 25°N (Miami, Cairo) | 54° | Workable |
| 35°S (Sydney, Santiago) | below horizon | Never rises |
Also worth imaging
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