* Back in the saddle! A series of mono images from 2022 *

One of my sharpest, deepest stacks ever, and I’m really pleased with it!

I decided to keep the core pretty bright in the original version, to show the distribution of power inside this mighty galaxy. PixInsight has some specialized tools to compress the dynamic range, which I used in a close-up crop to show the dark dust lanes around the galactic nucleus. (Rev. B)

Technical
This is a High-Dynamic Range combination of both 30 second and 300 second exposures. ​​​​​​​With drizzle, the  galaxy easily fills the frame. Another crazy achievement: the telescope stayed outside for several consecutive days and I did not touch the focuser at all between sessions. Focus was spot-on each night and some sub-frames even showed a FWHM of less than 2 arcseconds, which is incredibly sharp! Very round stars as well (for my standards), a testament to good collimation and tracking. 

Comparing my M81 data with the famous Digitized Sky Survey (DSS)
The Palomar observatory used a 48 inch Schmidt telescope and photographic emulsion plates to construct a reference of the entire sky between the 1980s and 1990s. All plates were scanned at a resolution of 1″ per pixel and are used extensively by astronomers. The region below is centered on Holmberg IX, a faint irregular dwarf galaxy and satellite of M81.



Some of the brighter stars in Holmberg IX are resolved, which really surprised me since this is a notoriously faint companion galaxy. The animation shows that several stars have moved significantly in the past 34 years, a phenomenon called proper motion of stars. My comparison also illustrates the enormous progress in the capabilities of amateur equipment, mostly driven by the development of CCD and CMOS cameras. Just a few decades ago, this realm of photography was exclusively for professional astronomers. 

I tried to match the stretch of both images but the brightness of some small stars is different and the galaxy contrast is also not entirely identical. I believe this is due to band pass differences: my Luminance filter passes all visible light, while the J-filter used in the Palomar plate passes blue-green light.