M101, the pinwheel galaxy – a spring classic

About the Object

Life was good to me (or was I good to myself?) and I got a full frame mono CMOS for my beloved Edge 11. Probably one of the best target for this combination is M101 - the pinwheel galaxy which substantially fills the available area. Conditions were not quite ideal (classical new-gear weather), but I was keen to play, so you take what you get. At the end I am quite happy with the overall result. Still fiddling with the setup and waiting for the narrow band filters - so sticking to LRGB for the time being. I may add Ha (and/or more exposure time) at a later stage.

Observation Notes

Data were taken on 2024 March 28, March 31, April 29, and April 30.

Note added in May 2025: I added 5.25h of Halpha data (taken on May 11 and 12)  and completely reprocessed the stack. Revision C shows the reprocessed LRGB, Revision D the corresponding HaLRGB and revision E an animated gif blinking between revisions C and D.

Note added in June 2025: I never was fully happy with the body of the galaxy: when separating stars and diffuse galaxy using StarXT, the stars in the galaxy body were removed as well, and later on, when blending the processed stars and the processed, contrast enhanced, body, the stars in the arm did not really pop out. So I change my workflow by putting a mask over the galaxy body except the bright foreground stars, and then run StarXT with the galaxy protected. As a result, the starless image contains the diffuse galaxy + the stars in the spiral arms of M101, while the star image only contains foreground stars. Then I processed (foreground) stars and galaxy (including the stars in m101) separately, as before. As a result of the exercise, the blue stars in the arms of M101 pop out much nicer. (Revision F and G for the image w/o and with Ha, respectively, revision H being an animated gif between rev F and G).

Technical Details

View the full-resolution image together with complete acquisition and processing details on AstroBin.