One of the most famous and photographed astronomical objects, the Whirlpool Galaxy is perhaps the finest example of the classic spiral "grand design." In fact, it was the first celestial object in which spiral structure was observed, by Irish astronomer Lord Rosse (William Parsons) in 1845. Note that we actually have here a pair of galaxies, involved in an intricate cosmic dance. The smaller galaxy, known only as NGC 5195 is actually behind the larger M51, as can be discerned by the dark clouds of dust in one of M51's spiral arms silhouetted against NGC 5195. Theories of how spiral arms form in galaxies indicate that it may actually be the influence of a close neighbor such as this one that gives rise to the arms in the first place. Another result of this gravitational tango is the throwing off of huge swaths of material from the galaxies into intergalactic space, seen here as the faint creamy "extra arms" extending away from the galaxies.