Celestial hemisphere:  Northern  ·  Constellation: Cassiopeia (Cas)  ·  Contains:  NGC 436  ·  NGC 457  ·  The star φCas
Owl Cluster and NGC 436 in Cassiopeia, Elisabeth Milne
Owl Cluster and NGC 436 in Cassiopeia
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Owl Cluster and NGC 436 in Cassiopeia

Owl Cluster and NGC 436 in Cassiopeia, Elisabeth Milne
Owl Cluster and NGC 436 in Cassiopeia
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Owl Cluster and NGC 436 in Cassiopeia

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Description

Caldwell 13 (NGC 457) is a young (20 million years old) open cluster approximately 8,000 – 8,500 light years away in the constellation of Cassiopeaia. It is often called the ‘Owl Cluster’ or the ‘ET Cluster’ because of the shape formed by the stars of the cluster, especially perhaps the large ‘eyes’ of the Owl (or ET). These ‘eyes’ are the double star φ Cassiopeiae. Yet, it seems likely that φ Cassiopeiae does not belong to the cluster: the double is estimated to be considerably closer to Earth - at a distance of 2,300 – 4,500 light years.

The cluster was discovered by William Herschel on 18 October 1787.

[Information from: O’Meara, SJ, The Caldwell Objects: Second Edition: Cambridge University Press – 2016.]

The image also shows NGC 436 – another open cluster in the constellation of Cassiopeia that was also discovered by William Herschel – this time on 3 November 1787. NGC 436 is around 9,800 light years distant and of a similar age to Caldwell 13. [Information: various Internet sources.]



This object was photographed from our home observatory in the UK between 3 and 13 December 2018.

Capture details:

Telescope: Skywatcher Esprit 120 with flattener

Camera: Moravian G2-8300

Filters: Baader RGB

Mount: Mesu 200

Red: 30 x 300s

Green: 30 x 300s

Blue: 30 x 300s

A total of 7 hours 30 minutes.

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Owl Cluster and NGC 436 in Cassiopeia, Elisabeth Milne

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