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: Similar to gravitational lensing involving quasars (click here) where an intermediate galaxy in the observer's line of sight distorts and magnifies the light from a distant quasar immediately behind the same line of sight, examples involving distant dim galaxies in lieue of quasars also exist and are commonly referred to as "Einstein ring galaxies" where the distortion of the more distant galaxy's light by an intermediate galaxy is so perfect that an illusionary ring is produced. The most extensive study involving Einstein ring galaxies is the work by Adam Bolton at the University of Hawaii (click here) who recently identified 70 such examples of gravitational lensing leading a perfect (Einstein) ring.

Note: For an interesting article on Einstein's ring galaxies, see also the discussion surrounding JVAS B1938+666 here.