Galaxies are perhaps one of the most attractive deep-sky objects to observe and photograph. They represent massive collections of dust, gas
and countless billions of stars and are best described as islands of space matter across the universe. They are characterized as being either
spiral or elliptical in nature and usually have a bright central core. Equally stunning to observe (with large-aperture telescopes) and image
are galaxy clusters which represent collections of gravitationally-bound groups of galaxies whose members number from tens to thousands and
which are classified on the basis of their richness (ie. number of galaxy members), shape (spherical, flat or irregular) and content (spiral
or elliptical). Charles Messier's list of deep-sky celestial gems includes approximately forty bright and large galaxies.
Our own galaxy, the Milky Way, represents a galaxy within the Local Group (of Galaxies)
numbering 30 galaxies in total, five million light years in diameter and which is moving in unison towards the constellation of Virgo. Other
prominent galaxies within the Local Group include Andromeda (150,000 light-years in diameter), Triangulum (40,000 light-years in diameter)
and the Large and Small Magellanic Clouds (30,000 and 20,000 light-years in diameter respectively). The center of the Local Group is believed
to lie between the Milky Way and the Andromeda Galaxy. The richest member of our Local Group is the Virgo Cluster which is believed to contain
approximately 2500 galaxies mostly elliptical in nature.
Note: NGC 147 in Cassiopeia is a dim dwarf spheroidal galaxy with an apparent magnitude of 9.5 and a surface
brightness of 14.3 mag/arcmin2. Discovered in 1829 by Herschel, this galaxy is a member of the
Local group of galaxies and forms an interesting physical and bound pair with
NGC 185 (UGC 396) which lies less than one degree away. Lying at a distance of 2.40 million light-years away, it has an apparent diameter of
13' by 9' and spans 10,500 light-years across. It is visible in amateur equipment as an elongated structure with a dim core and with a mag
13.5 star just to its north.
NGC 147 is also one of the approximately 60 galaxies for which (extragalactic) globular clusters have been identified with its four clusters
ranging in magnitude from 16.98 to 21.10 and dated to be 9+1 billion years-old (click
here and here).
Please click on the image below to display in higher resolution (1335 x 900)