The 51st entry in Charles Messier's famous catalog is perhaps the original spiral nebula--a large galaxy with a well defined spiral structure also cataloged as NGC 5194. Over 60,000 light-years across, M51's spiral arms and dust lanes clearly sweep in front of its companion galaxy, NGC 5195. The pair are about 31 million light-years distant. Not far on the sky from the handle of the Big Dipper, they officially lie within the boundaries of the small constellation Canes Venatici.
NASA, Hubble Heritage Team, (STScI/AURA), ESA, S. Beckwith (STScI)
