Caldwell 13 or NGC 457 is a beautiful open star cluster in the constellation Cassiopeia that’s known as the Owl Cluster.
The star cluster is also sometimes called the ‘ET Cluster’, given its supposed similarity in appearance to the famous extra-terrestrial in Steven Spielberg’s famous sci-fi film.
The Owl Cluster is located 7,900 lightyears away and is thought to have formed about 20 million years ago.
C13 Owl Cluster by Mark Griffith, Swindon, Wiltshire, UK. Equipment: GSO 8″ Richey-Chretien Optical tube, Skywatcher NEQ6 pro mount, Atik 383L+ camera, motorised filter wheel and Astronomik LRGB filters.
The Owl Cluster was discovered in 1787 by astronomer William Herschel and is a favourite target of astronomers obsvering the region around Cassiopeia with a telescope.
It’s included in the famous Caldwell Catalogue, compiled by the late Sir Patrick Moore, and info on how to find it can be found in our guide to Caldwell Catalogue (it’s number 4 on the list).
NGC 457 is an example of an open star cluster. Open star clusters are somewhat different from globular clusters, which are some of the oldest objects in the Universe.
Owl Cluster by Jaspal Chadha, London, UK. Equipment: Altair Astro RC 250TT, Focal reducer, QHY9S MONO CCD, Ioptron CEM60 mount, Chroma Technology filters.
Firstly, open star clusters are much younger – less than 10 billion years old – and secondly, they contain hundreds or thousands of stars, whereas globular clusters can contain up to hundreds of thousands.
Below is a selection of images of the Owl Cluster captured by BBC Sky at Night Magazine readers and astrophotographers.
For advice on imaging a cluster like this, read our guide on how to photograph stars or our beginner’s guide to astrophotography.
And don’t forget to send us your images or share them with us via Facebook, Twitter or Instagram.
The Owl Cluster, by Steve Pastor, New Mexico, US, 13 December 2018
Equipment: SBIG STF-8300 cooled mono CCD camera, RC Optical Systems 12.5-inch f/9 Ritchey Chrétien, Paramount ME mount.
NGC457 – The ET Cluster in Cassiopeia by Bill McSorley, Leeds, UK. Equipment: SW 150P Newtonian, EQ5 GoTo Mount, QHY8L cooled ccd.
NGC457 The Owl (or ET) Cluster by Chris Duffy, Consett, Co Durham, UK. Equipment: Canon 1100d, Skywatcher 130PDS EQ5 Pro Mount, ASI120MC, 50mm Finder Guider.
C13 Owl Cluster by Mark Griffith, Swindon, Wiltshire, UK. Equipment: Celestron C11 Sct, Skywatcher NEQ6 pro mount, Atik 383L+ camera, motorised filter wheel and Astronomik filters.
Owl Cluster by Jaspal Chadha, London, UK. Equipment: Skywatcher Espirt 100ED, Ioptron CEM60, Altair Astro LRGB, QSI 690 CCD.
E.T Cluster by Jaspal Chadha, London, UK. Equipment: Takahashi 130, QSI 690 ccd, LRGB, Ioptron CEM60 Mount.