For the record, mosaics aren't my favorite thing. For the full record, this is my second, so I likely have much yet to learn, but... not my fav. It's been over seven years since I imaged M31 - the hiatus partly due to my moving to a focal length and camera that could no longer frame it, and partly due to an aversion to mosaics (apparently for good reason). This is a 4 panel and to be fair, the luminance panels went together rather smoothly in PI, with what I'd consider minor stitching artifacts (some doubled stars near the center due to distortion and very few pinched stars at the periphery). The chrominance data on the other hand was a veritable hellscape of gradients, aberrations, and more gradients. Try as I might, two attempts to stitch these together in PI and one in APP, gave me nothing but trash despite tweaking every normalization and gradient reduction routine I could throw at it, pre and post facto. In the end, I pulled out my mobile rig - AT65EDQ, QSI683, HEQ5 - and went to town on the RBG over two nights, battling rig issues, clouds, and a particularly needy cat. I also grabbed Ha data as well. I had to blend this chrominance with the mosaic chrominance at the periphery as the rotation wasn't exactly the same and the field is slightly smaller. PI thankfully made quick work of all the alignments and distortion, however I did have some slightly misaligned color channels from unequal distortion between the mosaic and the 683. Lots of spot fixes for those. So, after a tour de force effort, I present the fruits of my labor. This is a 25% reduction to work well with Abin. I'm pleased with the resolution and finally how those colors came out.

One of my goals and a nice bonus was to resolve the star that changed the universe (quite literally), Hubble's landmark VAR!. Hubble took advantage of the central work of Henrietta Leavitt, whose seminal discovery of the period-luminosity relationship of Cepheid variables lead to a standard candle with which to gauge distances. Hubble discovered a cepheid variable in M31 and used the (now appropriately coined) "Leavitt Law" to determine that the "Andromeda Nebula" was in fact its own island universe after all, dramatically expanding the known universe for us and forever changing our sense of scale and organization of the cosmos. Hubble had previously inked "N" on the original glass plate used to photograph M31, mistaking this for a Nova, but later corrected this to "VAR!" throwing in his excitement for all to enjoy. You can enjoy my little Easter egg, Hubble's annotated variable, at ~7:00 from the core just above the outer dust lane. There are some very interesting star forming regions in the area. 

Web sites:

StellarSolace

Facebook page