Galaxies are everywhere, including within the unlikely Winter Milky Way territory of Cassiopeia. There are three well known though rather elusive Local Group galaxies found here. NGC 147 and 185 are satellites of the mighty Andromeda Galaxy (Messier 31), the Local Group’s dominant force. Though IC10 is not gravitationally bound to Messier 31, it appears to be part of the Andromeda subgroup, along with Messier 33, the Triangulum Galaxy.
NGC 147: a companion of the mighty Andromeda Galaxy
Dwarf spheroidal galaxy NGC 147 (Caldwell 17) is one of mighty Andromeda Galaxy’s (Messier 31) retinue. NGC 147 is located around two degrees west of magnitude +4.5 omicron Cassiopeia. It is gravitationally bound to and orbits Messier 31.
NGC 147 spans a substantial 13’ x 8.1’ and has an encouraging catalogued magnitude of +9.5. However, it suffers from what Luginbuhl and Skiff’s Observing Handbook and Catalogue of Deep-Sky Objects describe as ‘exceptionally low surface brightness’. This, they say, renders it ‘difficult to see’ in a 300mm (12-inch) telescope.
NGC 185: a dwarf elliptical
NGC 185 (Caldwell 18) is marginally is brightest (magnitude +9.2) and easiest to see of the galaxy trio. Seven degrees due north of Messier 31 lies fifth-magnitude omicron Cassiopeiae and just a degree west lies NGC 185, with NGC147 placed just under a degree farther to the west.
As galaxies go, NGC 185 is a dwarf elliptical (class dE3 pec) that has quite a large apparent diameter of 11’ x 9.8’, a size owing entirely to its proximity (~ 2 million light years) to us; physically, it’s no larger than 10,000 light years across.
NGC 185 can be swept up as a ghostly, circular patch of light about 4’ across through a 100-150mm (four- to six-inches) telescope, though there’s little if any structure on show other than its brighter core.
Starburst IC10
IC 10’s morphological classification is a dwarf irregular galaxy and termed a ‘starburst’ galaxy (referencing the intense star formation taking place there), the only one of its kind found in our Local Group of Galaxies.
IC 10 is easy to find, lying just 1.5 degrees east of Caph (beta Cas, magnitude +2.3). This places it in the middle of the winter Milky Way, which means interstellar dust and gas lying along its line-of-sight heavily obscures our view. Nevertheless, it still shines at a reasonable magnitude +10.3 and spans 5.1’ x 4.3’, as seen in images.
A 150mm (six-inch) telescope can pick up IC 10 in a dark and transparent sky as a small, featureless patch of light orientated south-east to north-west. A 300mm (12-inch) ‘scope shows some granulation and no obvious nucleus across its 4’ x 2’ form.
All three galaxies are circumpolar from UK shores and transit the southern meridian (culminate) at about the same time (midnight BST at mid-October) almost right at the zenith (overhead).
source: astronomynow.com