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Contains:  NGC 457, NGC 436, The star φCas
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Owl Cluster and NGC 436 in Cassiopeia, 


            Elisabeth Milne
Owl Cluster and NGC 436 in Cassiopeia

Owl Cluster and NGC 436 in Cassiopeia

Technical card

Resolution: 3543x2634

Dates:Dec. 13, 2018

Baader B: 30x300" bin 1x1
Baader G: 30x300" bin 1x1
Baader R: 30x300" bin 1x1

Integration: 7.5 hours

Avg. Moon age: 5.62 days

Avg. Moon phase: 31.64% job: 2539375

RA center: 19.665 degrees

DEC center: 58.476 degrees

Pixel scale: 1.203 arcsec/pixel

Orientation: 270.531 degrees

Field radius: 0.738 degrees

Locations: Home, Nottinghamshire, Nottinghamshire, United Kingdom

Data source: Unknown


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.



Elisabeth Milne
License: None (All rights reserved)


  • Owl Cluster and NGC 436 in Cassiopeia, 


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


            Elisabeth Milne

Sky plot

Sky plot


Owl Cluster and NGC 436 in Cassiopeia, 


            Elisabeth Milne

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