Bubbles In Space

With Cassiopeia on the rise again, now is a good time to start imaging in the region, despite the shorter summer nights and lack of full astronomical darkness. And as I’m now moving forward with narrowband imaging, the Bubble Nebula is a fine target to go for.

The Bubble Nebula, (or NGC 7635 to give it it’s New Galactic Catalogue designation) is an Hii region emission nebula. An Hii region is a region of interstellar atomic hydrogen that is ionised.

The first night didn’t go as well as I hoped with the 72ED on the Star Adventurer. Either I was out of balance or I wasn’t as level as I thought I was but of the over two hours of data that I accrued, slightly less than an hour was usable. The saving grace is that it’s reasonably bright at magnitude 10, and with it being an emission nebula, it’s well suited to the ZWO Duo Narrowband Filter.

The second night went even worse…I shot completely the wrong target, even with platesolving! Although in fairness I did capture a quite nice emission nebula right next door, it still wasn’t the target I was after.

NGC 7538, next door to NGC 7635. Oops!!

The third night went much smoother, and I was able to increase my total exposure time to a massive 2 and a half hours…I REALLY need to get the main rig running again! I imaged for almost 3 hrs and managed to keep just 72 minutes of the data. I know I have myself to blame here with overloading the tracking mount, so I shouldn’t really complain too much. But where, less than a year ago, I was managing to push 5 minute subs with it, it’s now struggling for a minute, and if anything I’ve actually improved how stable it is. So I’m at a loss as to why it should now be as temperamental as it is.

Anyway, the fourth (and final night) has gone quite well. It came at the end of the better part of a week of clear skies around mid-July, during which time I mainly got some narrowband data on M27 at home, which I’ll post in another blog.

The skies on the final night weren’t been the best. Seeing and transparency were pretty unimpressive. Whilst the sky during the day might look nice and blue, there was still a fair amount of haze and rubbish in the atmosphere. The subs don’t look too bad though, and the ones I’ve checked so far seem to indicate the mount was more or less behaving itself.

Post Processing

After trawling through all four nights I’ve managed to keep 405 frames, all taken using the ZWO Duo Narrowband Filter with the 72ED and ZWO ASI17MC. This means I have a total of 405 minutes worth of total data, which equates to 6 hrs 45 minutes. The best part is I’ve clearly seen the difference between imaging purely in broadband and narrowband, the biggest benefit so far being that I haven’t had to contend with either light pollution or moonwash.

The frames are stacked into AstroPixel Processor, for three integration runs. The first one is to pull out the RGB. The second one is for the Ha (or hydrogen alpha), whilst the third is to extract the Oiii (oxygen). I save each one as a TIFF file, without cropping, and then open them in Photoshop. From there I copy the Ha and Oiii into the red and green/blue channels respectively. Not entirely sure what that’s called – is it HOORGB? But from that point I edit and process as normal. The question is, should I process the channels individually? I’ll try that method as well at some point and see if it gives me a better final image.

The final image is something I’m pretty happy with, considering the limitations of both the mount and the camera, and I’m quite sure I’ll add more data to it at some point as well. But for now, this is my Bubble Nebula done for the time being as I move onto another project.

Many thanks for reading. Keep looking up and, for now, clear skies!

NGC 7635 Bubble Nebula in HOO. 6hrs 45mins integration

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