A Tour of M51 spiral galaxy.
M51 (NGC 5194) The Whirlpool Galaxy is a grand design spiral galaxy located in the constellation of Canes Venatici, "the Hunting Dogs". It is one of the most famous galaxies in the sky, appearing face-on when viewed from Earth. At magnitude 8.4, it's relatively bright and visible in binoculars especially from a dark site. It has a much smaller dwarf companion NGC 5195 and together they are well-known as the finest and most studied example of an interacting galaxy pair.
M51 was one of Charles Messier original discoveries on October 13, 1773 while his friend Pierre Mechain discovered NGC 5195 on March 20, 1781. Messier described M51 as a faint nebula without stars that was difficult to see. In his catalogue of 1781, Messier describes both M51 and NGC 5195 in the same note and hence there is some confusion over the exact designation of M51. Is he referring to M51 as just the larger galaxy or does he actually mean the pair? If it's the pair then NGC 5194 is sometimes referred to as "M51A", with NGC 5195 separately known as "M51B".
Canes Venatici is a small northern constellation of faint stars that was created by Johannes Hevelius in the 17th century. Apart from its brightest star Cor Caroli ([eth] CVn - mag. 2.9), the constellation contains no stars brighter than 4th magnitude. However, locating M51 isn't difficult as it positioned towards the northeast border of Canes Venatici and only a few degrees from the handle of the seven stars that form the famous "Plough" or "Big Dipper" asterism of Ursa Major.
To locate M51, first identify Alkaid ([eth][cedilla] UMa - mag 1.9) the end star of the handle of the bowl of the "Plough". Located 3 degrees directly west of Alkaid is magnitude 4.5 star 24 UMa. Positioned a degree to the northeast of 24 UMa is a magnitude 6.5 star. Now imagine a line from this star to 24 UMa and then continue it southwards for a further two degrees. This leads to a triangle of stars of magnitudes 7.1, 7.1 and 7.5. All three stars are easily visible in binoculars with M51 located just west of the southernmost star.
-Thursday, June 19, 2014 SOURCE CIHAN
-VAR of M51 spiral galaxy
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