When trying to observe considered one of Cassiopeia’s wonderland of shiny open clusters, don’t make the frequent and comprehensible mistake of heading within the course of both of the constellation’s Messier-designated clusters, Messier 52 or Messier 103, positive clusters although they undoubtably are! As a substitute, your first port of name needs to be NGC 457 (Caldwell 13), an attention grabbing open cluster with two well-known nicknames, the Owl Cluster and the extra lately acquired ET Cluster. In its time it’s additionally been referred to as the Phi Cassiopeiae Cluster (see beneath).
Shining brightly at magnitude +6.4, brighter than both of the Messier clusters, NGC 457 may be seen by eagle-eyed (or ought to I say owl-eyed?!) people at pristine observing places. For almost all of UK, it’s a simple object for 10 × 50 binoculars, showing as a fuzzy patch of sunshine, and a small telescope will readily select (resolve) a few dozen of its member stars.
If all this excellent news isn’t sufficient, the Owl is circumpolar (never-setting) from the UK and peaks in altitude on the zenith (overhead), which signifies that it may be noticed all evening.
Methods to observe:
NGC 457’s location is simple to pin down, owing to the fifth-magnitude star phi (φ) Cassiopeiae (Cas), now thought of a cluster member and serving as one of many Owl’s eyes, mendacity handily simply two levels south-south-east of Ruchbah (delta [δ] Cas). Cassiopeia’s well-known and shiny ‘W’ asterism (star sample), which incorporates Ruchbah, is without doubt one of the most recognisable in your entire sky.
By dusk, which happens by 9pm BST from London, Cassiopeia is positioned 45 levels excessive within the east-north-east and climbing. NGC 457 lies excessive overhead at across the small hours.
A small telescope of about 80mm [~ three inches) in aperture can resolve around 25 individual stars within NGC 457, rising to nearly 50 through a telescope in the 150mm (six-inch) class, spread out across an apparent diameter of 13’. These cluster members, of which there are thought to be around 200 in total, are arranged in noticeable lines and curves, which give rise to its Owl moniker and makes it an attractive sight.
The aforementioned star phi and the nearby star (to the south-west) magnitude +7 HIP 6229 represent the bird’s eyes, though they also remind some of the eyes of ET, the Extra-Terrestrial, Stephen Spielberg’s gentle alien creation.
