Here's the section on M51 from my post at https://www.cloudyni...mers/?p=4592919
M51 (the Whirlpool Galaxy)
M51 (NGC 5194, integrated magnitude=8.4, surface brightness=12.6 magnitudes per square arcminute), a type SA(s)bc pec face-on spiral galaxy, and its irregular companion M51b or NGC 5195 (magnitude 9.6, surface brightness=13.1 magnitudes per square arcminute) are perhaps the most prominent example of an interacting pair of galaxies. They are best seen in the spring.
Due to the work of Lord Rosse In 1845, M51 was the first galaxy to be recognized as having a spiral shape. Of course, M51 was merely a "nebula" at that time, which was long before galaxies were determined to be objects external to the Milky Way.
M51 and NGC 5195 may be part of the M101 group of galaxies. Three supernovae have occurred in M51: SN 1994I, SN 2005cs, and SN 2011dh.
To star-hop to the Whirlpool Galaxy, proceed southwest from Alkaid (Eta Ursae Majoris), the final star in the Big Dipper's handle, to the fifth-magnitude star 24 Canum Venaticorum. Continue southwest to an isosceles triangle of seventh-magnitude stars. M51 and NGC 5195 lie just to the south of the triangle, approximately 3.5 degrees from Alkaid and 1/4 of the way to Cor Caroli (Alpha Canum Venaticorum).
Star-hops to M51 can be found at the following sites:
Information on the Whirlpool Galaxy and a finder chart can be found at https://freestarcharts.com/messier-51
Telrad finder charts for M51 are available at the following sites:
For further information on the Whirlpool Galaxy, consult these sites: