The Pinwheel Galaxy (also known as Messier 101, M101 or NGC 5457) is a face-on spiral galaxy distanced 21 million light-years away in the constellation Ursa Major, first discovered by Pierre Méchain on March 27, 1781, and communicated to Charles Messier who verified its position for inclusion in the Messier Catalogue as one of its final entries.

M101 is a large galaxy comparable in size to the Milky Way. With a diameter of 170,000 light-years it is roughly equal the size of the Milky Way. It has a disk mass on the order of 100 billion solar masses, along with a small central bulge of about 3 billion solar masses.

M101 is noted for its high population of H II regions, many of which are very large and bright. H II regions usually accompany the enormous clouds of high density molecular hydrogen gas contracting under their own gravitational force where stars form. H II regions are ionized by large numbers of extremely bright and hot young stars; those in M101 are capable of creating hot superbubbles. In a 1990 study, 1264 H II regions were cataloged in the galaxy. Three are prominent enough to receive New General Catalogue numbers - NGC 5461, NGC 5462, and NGC 5471.

M101 is asymmetrical due to the tidal forces from interactions with its companion galaxies. These gravitational interactions compress interstellar hydrogen gas, which then triggers strong star formation activity in M101's spiral arms that can be detected in ultraviolet images.--Wiki

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Way more Ha on this one than I needed, but it was around full moon and I needed to do some testing on the mount, so I hammered away at the Ha. It was pretty cool seeing so much of the galaxy showing up in Ha. The mount seems to be working fine now since adding the counterweight to offset the weight of the motors hanging off the other side of the mount, and tightening the clutches as much as I could. Clutches must be under-engineered for these massive gears, or it could just be that the levers are so small that it makes it hard to get them tight enough. Some people have removed the levers and use a 1/4" ratchet to tighten the clutches down. I wont do this just yet since I have an observatory. I defined a new park position that has the scope laying over on its side so I can open and close the roof without needing to loosen and tighten the clutches anymore.

Revision B is annotated. Lots of galaxies in this background. I mixed Ha into the red channel at 15% Ha/85% Red.