When I saw the amazing image of Andromeda's Oiii emission arc by @Marcel Drechsler, @Xavier Strottner, and @Yann SAINTY in the beginning of 2023, I was blown away. Immediately, I knew I had to try capturing this magnificient structure myself.

It was clear from the start, this endeavour would need massive integration time, especially due to my Bortle 6 backyard. I decided to throw everything I have at this thing meaning dedicating the entire target season to M31, i.e. starting in July 2023 and suck up photons until January 2024. This is a tremendous challenge for impatient astrophotographers like me. Watching other gems fly by and keep shooting the same target for months after months requires lots of patience. Luckily, my second rig allowed me to continue shooting other targets while Mission: Andromeda kept running.

I chose my trusty Esprit 100 as the OTA of choice for this project. To elevate my chances, I powered it up with the 0.75x Riccardi reducer to F/4. And even at this speed, the arc was nowhere to be seen as the total integration count went up steadily. After around 30 hours, I could make out a faint structure in a starless, de-noised and ridiculously stretched O3 master. That was all I needed to proceed and pull through until January.

In the end, there is a total of 40 nights over Andromeda's entire season here in Augsburg that went into this image.

Breakdown of the nights:

Jul    1
Aug    3
Sep    15
Oct    11
Nov    3
Dec    4    
Jan    3

The winter months were really bad in terms of clear nights, but I took any chance I got to set to set up the rig. Thanks to the amazing September and October, this project was a success.

Eventually, I was able to shoot 100h of Oxygen3 and 50h of Hydrogen. To say I feel gifted for such an immense integration time opportunity is an understatement. Even though winter left me hanging, summer and fall did the trick. I feel with all those with worse skies that are still full of determination and motivation. You are awesome!

Pre-processing 2274 images was also no easy feat, especially since I planned on drizzling the image at 2x which meant I had to keep all files during pre-processing. In the end, we are talking about 720GB worth of data before hitting the drizzle button. My new M2 Macbook fought through these mountains of data like a champ!

After all these challenges, the integrated masters were finished and the real challenge began: Processing the image.
I had to pull every trick I learned in the past two and a half years out of my sleeve. The Oiii arc is so faint it is almost insulting. The arc in the presented image is boosted to a large extent so it can even punch through. Ou4 is challenging from Bortle 6, but this thing... is a totally different beast.
I have absolutely no idea how the team managed to resolve such fine structures in the arc. It is beyond me, maddest respect to Marcel, Xavier, and Yann. We are ash, we are dust.

In addition, the Hydrogen gas between Earth and M31 is also tough to bring out well. The hydrogen channel also shows great structure in the galaxy core, which is why I decided to integrate this into the image's luminance. I have seen some images of M31's core in Ha that left me in awe, hopefully more people with large focal lengths and apertures will pick this up and spoil us with images of this amazing core region.

This is the deepest image I have taken and I doubt anything will come close in the foreseeable future. But it was an amazing ride.

Thank you all for your great images and discoveries that keep me shooting.

Clear skies to you all!
Dominik