|M51 "Whirlpool Galaxy": Interacting Galaxy Pair (Canes Venatici) RA: 13h 29.9m / DEC: +47° 11'.8|
Instrument: 10-inch Starfinder
M51 is an interacting galaxy pair in Canes Venatici just off the end of the handle of the Big Dipper. Their NGC designations are 5194 and 5195. I begin my hop to M51 at the star marking the end of the dipper's handle, 1.9 magnitude Alkaid. Slew west-southwest 2.2 degrees to 4.7 magnitude 24 Canum Venaticorum. From there, move 1.5 degrees south-southwest to a triangular arrangement of 7th magnitude stars. M51 sits along the southwest side of the triangle and is visible in my 8X50 finder scope under dark Arizona skies. M51 has an undeserved reputation as a difficult object. The main component, NGC 5194, has a relatively high surface brightness making it an easy detection with 6-inches or more aperture under typical suburban skies. The difficulty comes when trying to observe this faint pair when they are swimming in the muddy air near the horizon. M51 is best viewed when the handle of the Big Dipper is riding high in the northern sky, typically during the late winter and early spring months of February through April.
NGC 5194 is the main component. This face-on spiral galaxy was discovered by Charles Messier in 1773. It shines at 8.4 magnitude and covers a 6' diameter area at 129X in my 10-inch. The spiral structure becomes evident in steady, dark skies. Two arms are visible as is a bright stellar core. Don't be misled by the bright star in the one spiral arm. It's not a supernova. The other spiral arm appears to bridge the gulf between NGC 5194 and NGC 5195, a 3'x2' 9.6 magnitude swatch of light. The spiral arm is actually in the foreground of the smaller galaxy. If this bridge is visible, spend some time looking for spiral structure and mottling in NGC 5194. As a side note, many amateurs assume NGC 5195 is not part of M51. Pierre Mechain discovered NGC 5195 in 1781 and his description, which clearly mentions both galaxies, was published in Messier's 1784 catalog. Because of this, some references identify NGC 5194 as M51a and NGC 5195 as M51b.
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Revised: February 14, 2002 [WDF]