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: The Whirlpool Galaxy in Canes Venatici is one of the most stunning showpieces of the evening sky and perhaps the best example of interacting galaxies. As indicated by the image below, aside from being a very impressive face-on spiral galaxy with distinct and highly resolved arms, it is cannibalizing a smaller galaxy (NGC 5195, M51B) in the immediate vicinity with a very clear and distinct "bridge" between them. Lying at a distance of 37 million light-years away, M51 has an apparent diameter of just over 10 arc-minutes and which represents a span of 70,000 light-years across. It is fairly bright (mag 8.5) with a bright core and is within easy reach of amateur equipment and especially under dark(er) skies. As a result of its interaction with NGC 5195, the Whirlpool Galaxy is not symmetric and has a slightly misplaced core which prompted Halton Arp to include this galaxy as "Arp 85" in his compilation of peculiar galaxies and under the sub-category of "Spiral with large HSB companion".

The Whirlpool Galaxy is a dominant member of the M101 group of galaxies and which includes M101 (mag 8.3), M63 (mag 9.3), NGC 5195 (mag 10.5), NGC 5585 (mag 11.2) and another ten smaller and dimmer member galaxies. M51 has been host to two supernovae (SN 1994I, mag 12.8; SN 2005cs, mag 13.5). This showpiece galaxy was discovered by Charles Messier in 1773 who described it as a "very faint nebula, without stars" whereas the companion galaxy (NGC 5195) was first discovered by Messier's associate Pierre Mechain in 1781.