In April 2022 I observed Messier 51, the Whirlpool Galaxy, through the night while I slept. This is an extremely popular object, but I have never been very satisfied with my images of it. To some extent I'd lost hope of ever getting a clean image of this object. I think my problems were with balancing the very bright parts of the galaxy with the extended and asymmetric halo.
M51, wide field image.
M51 close up (cropped version of image above)
Messier 51 is quite bright and easily observed. Unsurprisingly, therefore, it was the first galaxy where spiral arms were clearly identified. M51 was discovered by Messier in 1773, but it was the Earl of Rosse in 1845 who produced a now-famous drawing of M51 showing both the spiral arms and the companion galaxy (see below).
Rosse used a 1.8m reflector for his observations, where I was limited to an 11" aperture RASA (30cm). That 1.8m telescope was known as the "Leviathan of Parsonstown" and was the largest telescope in the world from 1845 through 1917. That thing weighted a ton! Actually it weighed more than a ton, 3 tons in fact.
Drawing by William Parsons, 3rd Earl of Rosse (Lord Rosse) - Unknown source, Public Domain, https://commons.wikimedia.org/w/index.php?curid=1529615
The Whirlpool Galaxy is in the constellation Canes Vanatici, or the Hunting Dogs. It is near Ursa Major, at a declination near the latitude of my observatory (+45) meaning that it is nearly at the zenith at times. As mentioned, it is relatively big and bright as seen from Earth, 11 by 7 arcminutes, because it is relatively close (for another galaxy) at 31 Million light-years away.
The Galactic Latitude of this object is 68deg: a G Latitude of 90deg would be looking entirely away from plane of the Milky Way, and a G. Latitude of 0 is along the plane of the Milky Way (i.e. at all the stars, dust and nebulae nearby). A G. Latitude of 68 means we are looking out of our galaxy and can see to great distances. A result of this is that there are many small galaxies in the field of view that lie behind the Whirlpool. The foreground stars will be in the Milky Way at distances up to around 1000 light-years (assuming a disk thickness of 2000). The Whirlpool is 31 Million light-years away, and the tiny galaxies seen are at much greater distances. Some of what we see as stars are likely the cores of very distant galaxies.
In this image we can see well-defined spiral arms and dust lanes. The bridge between the main galaxy and its companion is clearly visible. The Whirlpool is very active in star-formation, likely due to the interaction with the companion.
The image here was produced by stacking over four hours of one-minute subframes (exposures) using the RASA11 telescope and the ZWO ASI6200 camera. Observed at Lac Teeples on the night of April 28 through 29, 2022.
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