Name: Messier 51 (NGC 5194) The Whirlpool Galaxy
Constellation - Canes Venatici
Size - 124,000 light years across (estimated),
Distance - 37 million light years (estimated),
Messier 51, also known as NGC 5194, is a star party favorite and has an interesting history. First observed by Charles Messier in October 1773, the spiral structure was not noted until 1845 by Lord Rosse. At the time of the discovery of the spiral structure, it was thought that Messier 51 was an example of a new solar system in formation within our Milky Way Galaxy. It was not until 1923 with the construction of larger, more powerful telescopes that Messier 51 was recognized as a distinct galaxy with its own stars and nebulae. Also shown in the above image is Messier 51's companion galaxy, NGC 5195. Although some have theorized that the two galaxies are connected. It is now generally recognized that they are two separate and distinct galaxies. However, it is believed that the prominent spiral structure of Messier 51 is due to its gravitational interaction with NGC 5195.
Messier 51 can be spotted with binoculars under a dark country sky. However, hints as to its spiral structure can only be detected under dark skies with telescopes of 8" and larger.
This incredibly detailed image was assembled from a 4-color mosaic data set which is available through the High Level Science Products page of the MAST archive. Here is a link to the M 51 page if you want to look at the data or try processing the data yourself - https://archive.stsci.edu/prepds/m51/
Camera: Advanced Camera for Surveys
F435W (B) 4 x 680s = 2720s 27.3 mB
F555W (V) 4 x 340s = 1360s 26.5 mV
F814W (I) 4 x 340s = 1360s 25.8 mI
F658N (H-alpha) 4 x 680s = 2720s
Color Assignments: red - blend of 50% F658N + 50% F814W, green - F555W, blue - F435W