Image 1 Caption: "This is the sketch made by William Parsons, 3rd Earl of Rosse, (1800-1867): (AKA Lord Rosse, AKA Himself of the Whirlpool Galaxy (AKA M51a/NGC 5194 and M51b/NGC 5195) in 1845." (Slightly edited.)

Features:

1. The Whirlpool Galaxy is in constellation Canes Venatici (the Hunting Dogs).

2. As the image hints, the Whirlpool Galaxy is actually 2 interacting galaxies: (1) NGC 5194/M51a (sometimes called the Whirlpool Galaxy just by itself) which is a large Sc spiral; (2) a smaller companion NGC 5195/M51b which is a peculiar barred lenticular (i.e., an SBO pec), but also classified as a dwarf galaxy.

3. The Whirlpool Galaxy is about 8.5 Mpc away and 20 kpc in diameter.

4. The spiral structure of some galaxies (historically known as the spiral nebulae) was first discovered from the Whirlpool Galaxy by Lord Rosse) in 1845 April at Birr Castle (Birr (formerly Parsonstown), County Offaly, Ireland) using the Leviathan of Parsonstown (reflector, primary diameter 1.83 m = 6 ft, operational 1845--c.1890). (Telescope file: telescope_leviathan.html; No-434--438). For more on the Leviathan, see Telescope file: telescope_leviathan.html.

5. Lord Rosse circulated a similar sketch at the 1845 June meeting of the British Association for the Advancement of Science.

   Lord Rosse's own caption for the similar sketch:

   Fig. 25 Herschell ??? sketched April 1845, carefully confirmed with original on different nights but no micrometer ??? Handed around the section at the Cambridge meeting

6. Lord Rosse was intensely interested in the spiral nebulae, but is NOT clear how he assessed the theory that they were other galaxies (Wikipedia: William Parsons, 3rd Earl of Rosse: Scientific studies; No-437). He did believe that nebulae (historical usage) were systems of stars at least in most cases (Wikipedia: William Parsons, 3rd Earl of Rosse: Scientific studies"). It seems unlikely he believed they all were since he himself discovered a planetary nebulae (No-436).

7. Lord Rosse and his collaborators with the Leviathan often obtained good accuracy with their sketches (No-437), but the fine detail is probably Impressionism. They were doing visual astronomy and then probably recreating what they'd seen as soon as possible by light of candle or kerosene lamp. However, even after the advent of astrophotography (advent 1840, but with only gradually improving technique in following decades) (Wikipedia: Astrophotography: History), the Leviathan sketches continued to be useful (No-437).

   

8. Image 2 Caption: A modern image of the Whirlpool Galaxy (AKA M51a/NGC 5194 and M51b/NGC 5195) in constellation Canes Venatici (the Hunting Dogs). M51a (the bigger galaxy) is a face-on grand design spiral galaxy.

9. Comparing Whirlpool Galaxy in Lord Rosse's sketch in Image 1 and in the modern Image 2 shows the quality his sketching.

10. Other sketches by Lord Rosse and collaborators can be seen by image googling lord rosse whirlpool galaxy.

11. After Lord Rosse's time, J.L.E. Dreyer (1852--1926) worked with the Leviathan 1874--1878. Dreyer would later compile the New General Catalogue (NGC: 1888) and the Index Catalogue (IC: 1895, 1908) of deep-sky objects (which include many spiral nebulae). Many nearby galaxies are still known by their NGC numbers or IC numbers.

Images:

1. Credit/Permission: William Parsons, 3rd Earl of Rosse (1800-1867), 1845 (uploaded to Wikipedia by User:Szdori~enwiki, 2007) / Public domain.
   Image link: Wikipedia: File:M51Sketch.jpg.
   
2. Credit/Permission: NASA, ESA, 2005 (uploaded to Wikimedia Commons by User:Laitche, 2008) / Public domain.
   Image link: Wikimedia Commons: File:Messier51 sRGB.jpg.