It’s been a very quiet few months since I took my Rosette Nebula image. The weather in the UK has been lousy to say the least, with only a handful of clear nights usable for imaging. However, that time of year has come round again, and it’s my first taste of it with my Sky-Watcher 130PDS!
If you want to skip ahead to just my report on my imaging sessions, just follow this link.
What is Galaxy Season?
I’m talking about one of astrophotography’s best and busiest times of the year! It’s when our own Milky Way, especially in the northern hemisphere, is least visible in the night sky. This in turn reveals the multitude of other galaxies in the observable universe, and has been coined ‘Galaxy Season’. It’s quite short lived and only runs from March, up until the beginning of May. The galaxies may be visible at other times of the year, but with the shorter nights and the return of the Milky Way core in the summer, those brief months are the best time to capture some stunning images.
The amount of galaxies that can be seen from a true dark sky site can be easily demonstrated in Stellarium. A string of galaxies running all the way from below Corvus, through Virgo and Coma Berenices and into Ursa Major can be seen below. Every single red and orange ring is an individual galaxy!
However, the galaxies that populate the night sky are usually very small and quite dim, especially from my light polluted (Bortle 6) back garden. Therefore darker skies, a larger telescope with more focal length and a wider aperture is required to make the most of them. Unfortunately, I’m only stuck with my 130PDS at the moment with its 650mm focal length. To make the most of it though I’m only planning to go for the larger galaxy clusters, such as the well-known Leo Triplet or Markarians Chain.
That’s one of the many reasons why astrophotographers have multiple telescopes that they swap and change throughout the year. Schmidt Cassegrain and EdgeHD’s are widely used for galaxies, and then widefield refractors with focal lengths of under 600mm are used for larger targets later in the year.
As can be seen below, both clusters fit well in my field of view (FoV) of my 130PDS and Canon 600Da.
The Imaging Sessions
The first session was on the night of the 16th March, and was only a test to see what I could capture now that I was guiding. I decided on a well know target, and one that I had captured before to compare it with.
Messier 51 – The Whirlpool Galaxy, is located in the constellation Canes Venatici, and is very distinctive due to the fact that it’s actually two galaxies, with one devouring the other. You can read my original post here. A year ago, I was only using 30-second unguided exposures, whereas now I’m capturing exposures of 300 seconds; 10x the length per exposure! However, it does help if my guiding was of any use…
For some reason, maybe the position of M51 near the zenith, my guiding was really inconsistent. My dithers were overshooting on their return, especially in declination again. This caused tracking errors greater than my pixel-scale of 1.36″ Arc-Seconds-per-pixel; this then affected the next exposure. Due to this, I was only able to capture 1 hour 20 minutes, which is nowhere near the exposure time that I would have wanted. Ideally I would want at least twice that time!
Unfortunately the weather rolled in for the next two weeks after that. But as I said, it was only meant to be a test. I’ll return to this target later in the year most likely and spend at least an entire night on it!
The next clear night was half a month later, on the 3rd April. The forecast was for clear skies all night long, and it didn’t disappoint. My target for this night was the Leo Triplet as it had risen to the point where I can see it all night, except for around 10 minutes where it passed behind my TV arial.
The night though wasn’t without it’s problems again unfortunately…
Firstly I turned my telescope towards the southern meridian, around 30º above the horizon and re-calibrated my mount in PHD2. I’ve been reading numerous forum posts about guiding, and also asking the members within the AstroBiscuit Discord server for any pointers. For anyone into astronomy and astrophotography, I highly recommend joining the AstroBiscuit server!
The first time I calibrated I increased the step size to 1500ms, however there was no improvement in the final guiding figures. So that idea was crossed off…
Second time I calibrated I returned to the PHD suggested step size of 850ms, however I balanced my declination axis mirror heavy. This was to ensure constant contact with the gears, similar to balancing east-heavy in right ascension. However, this also yielded no improvement, and was actually causing the guiding graph to slowly slope downward. So that ideas was also crossed off…
Third time lucky! I rebalanced the declination equally again and just opted for east-heavy in the right ascension axis. This time after a small recovery period to let everything settle down, I was getting an average RMS error of around 0.64 Arc-Seconds. I can most certainly live with that!
Also, the first meridian flip occurred since I’ve been using the Nightly builds, which has apparently had problems. I’m pleased to confirm thought that everything ran smoothly during and after the flip. The telescope flipped to the other side, re-centred my target, automatically chose a new guide star and re-started guiding again. It also allowed me to quickly dash outside and re-balance the counterweight before it started guiding. So at least I know that it works flawlessly now and don’t need to worry about that for the future!
At 2:30AM, everything was running so smoothly I actually decided to go to bed for a couple of hours and wake up at 4:00AM to replace the lens cap and start my dark and bias frames. Everything ran spectacularly, finishing everything at 6:30AM. The last few frames were unusable though unfortunately due to light-leak into the optical tube. Even so, I managed to capture 45 light frames (41 stacked), 22 dark frames, 50 bias frames and finally 30 flat frames taken the following morning. This produced a total exposure length of 3 hours 25 minutes!
On the whole, I’m very pleased with this image. The colours that I’ve been able to capture in M66 (bottom right) and M65 (top right) are absolutely stunning! My full spectrum camera certainly captured the hydrogen alpha response in them. It’s just a shame NGC 3628 – The Hamburg Galaxy, turned out a little noisy and pixelated. I suppose the saying’s true, you are your own worst critic!
I’ll stick with my modified DSLR for now, but I can quickly see me upgrading to a cooled CCD camera where the noise is much lower. But firstly I need to sort out my problematic EQ5 Pro, which is causing me most of the headaches at the moment. The mount is the workhorse of the whole system, and if that’s not upto the task it has a knock-on effect with the rest of the kit.
I either spend a pretty penny and get a new mount, or I get my EQ5 professionally hypertuned. Decisions, decisions!
It looks like the clouds have rolled in and are here to stay for the next week. So that looks like the end of the clear nights for the time being unfortunately. However, it gives me time to plan my next imaging session!
So till next time, clear skies!