Aside from maybe the excellent Pleiades open cluster in Taurus, the magnificent pair of open clusters forming the Double Cluster in Perseus is the best in its class at mid-northern latitudes. Formally categorised as NGC 869 and NGC 884 (h and chi [χ] Persei, respectively), both cluster rivals or eclipses the overwhelming majority of open clusters, together with these of the Messier selection. As a pair although, the Double Cluster is among the most gorgeous of deep-sky objects in the complete sky.
The Double Cluster might be spied with out optical help on the perfect of nights at a dark-sky location, however a never-to-be-forgotten sight awaits via a pair of binoculars or a small telescope – the sector of view strewn with myriad, sparking jewels of various brightness and color set towards a deep velvet backdrop. One may go so far as to argue that solely the Moon gives a finer binocular view! That is an object the place smaller is greatest: an 80mm, f/5 refractor at 40× frames the pair, overlaying a level throughout aspect by aspect, properly.
The Double Cluster is straightforward to seek out; mendacity near Perseus’ northern boundary with Cassiopeia, the latter’s well-known ‘W’ asterism might be put to good use as a celestial signpost. First, find the central star of the 5 stars within the ‘W’, gamma (γ, magazine. +2.1) after which Ruchbah (delta [δ], +2.7), the subsequent star eastwards. In case you sweep eastwards by roughly two lengths of an imaginary line between the 2 stars (roughly seven levels in total), then it’s best to land on the Double Cluster with little problem.
Every cluster spans about 30 arcminutes throughout, the identical measurement as the complete Moon. NGC 869, the extra westerly of the 2, has a barely extra concentrated core than NGC 884 and is brighter total too, with an built-in magazine. of +5.3 versus its companion’s +6.1. A pair of 10×50 binoculars simply resolves most of stars mendacity in each clusters, which vary in magnitude from +7 to +10.
On early November nights, the Double Cluster culminates very near the zenith (it’s circumpolar [never setting] from the UK), the place the sky is at its most clear and regular, and on the reasonably-sociable hour of about 11pm.
