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Owl Cluster (NGC 457)
open cluster in Cassiopeia
The Owl Cluster, or ET Cluster, is an open cluster in Cassiopeia with two bright stars that look like the eyes of an owl, and curved lines of stars like outstretched wings. It is a charming, easy target.
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// Key facts
- Catalog
- NGC 457
- Also known as
- C 13, Caldwell 13
- Type
- open cluster
- Constellation
- Cassiopeia
- Size
- 13′ across
- Brightness
- Magnitude 6.4
- Distance
- roughly 8,000 to 9,000 light-years
- Peak month (any location)
- Oct
- Typical prime months
- Jul to Dec
- Difficulty
- Beginner
- Filter
- No filter (broadband)
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How to image Owl Cluster
- Use 400 to 800 mm; it is about 13 arcminutes across.
- No filter is needed. Good focus keeps the stars tight.
- Cassiopeia is high in the north on autumn evenings.
Framing: what focal length?
NGC 457 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 16% |
| 2,000 mm | about 32% |
| 3,000 mm | about 48% |
How high does it climb from your latitude?
The highest point NGC 457 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) | 87° | High in the sky |
| 45°N (Minneapolis, Milan) | 77° | High in the sky |
| 35°N (Los Angeles, Tokyo) | 67° | High in the sky |
| 25°N (Miami, Cairo) | 57° | Workable |
| 35°S (Sydney, Santiago) | below horizon | Never rises |
Also worth imaging
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