It’s been an entire month since I have been able to get out and do some astrophotography. May this year has been a complete washout, with the met office saying that by halfway through the month, some areas of the UK had already passed their predicted monthly rainfall! With the weather over the past week slowly starting to improve, and temperatures increasing into the low 20ºC’s, this brought back the clear nights once again; welcome news to many in the astro community here in the UK.
However, during that month break we also lost astronomical darkness on the 18th May. For those who don’t know, this means that the night sky never gets truly dark and therefore in perpetual daylight. Not as bad as Scandinavia where the sun never sets, but if you look towards the north during the middle of the night, there’s always a light blue glow on the horizon. Imaging during this period is still possible of course, but it’s increasing more difficult the closer we get to the summer solstice. The warmer nights also cause more issues with thermal noise, especially on DSLR’s like mine. This is where people with dedicated cameras are fortunate, as they can cool their sensor down to below 0ºC. During these months with no brightness, It’s usually best to stick to bright objects like Globular Clusters or really bright galaxies like M31, M81 & M82 for example. Of course though, I don’t heed my own advice…
As nautical twilight begins around 11:30PM, the summer targets are fast beginning to rise in the east. Lyra, Cygnus and Cepheus are quickly rising towards the zenith as the night progresses on, with Pegasus and then the Andromeda Galaxy, quick on their tail.
I personally love the constellation Cygnus, as there’s so many bright and wonderful targets hiding amongst its wings. The most well known would be the east and west veil nebulas, a supernova remnant.. Another favourite target is the Crescent Nebula, which I’ve taken previously and want to re-visit in the future; might even be this year if fortune’s favour the bold!
However, for a change I’m going to follow my previous advice of ploughing tonnes of data into a single target. So I’m aiming for around the 40 hour mark on the Cygnus Wall in NGC 7000, the North America Nebula. This region of the nebula mostly resembles Mexico and Central America in the grand scheme of things. The whole area is an intense cloud of ionised Hydrogen, which emits Hydrogen-Alpha, among Sulphur-II and Oxygen-III, lending it self to be imaged in the Hubble palette of SHO. If only I could afford a mono camera and narrowband filters!
The light that has been emitted from this nebula has been traveling for 2,590 years. To put that into perspective, that’s around the time the first Egyptian dynasty was founded by Menes in the city Memphis! It’s utterly mind blowing!
Anyway, to the session!
I set up in the usual spot in the middle of my back garden and polar aligned as per usual. This new mount is an absolute breeze to polar align, and was fully set up in less than two minutes. At this point, it still wasn’t dark and only the brightest stars of Vega and Arcturus were visible. However, this gave me a great opportunity to get focused nice and early.
As you can see, the sky wasn’t clear to the west, however is was completely clear eastwards, fortunately where my target was located.
Using my Bahtinov mask and Live View on the back of my DSLR, it was only a very slight adjustment to get the line in the middle of the crosses. Just for a bit of fun, I tried a 10 second exposure to really test the mask. Using the Bahtinov Mask Tool in N.I.NA. to measure the spikes, I managed to get it pretty much spot on, with my focus error only being 0.21 pixels.
Although the sky looked clear to the naked eye, it was like a veil had been put over everything. My guiding reflected that as the total error was up around he 0.8″-1.0″ Total RMS mark; around double of what it usually is. That figure is still acceptable for my setup though, as it’s below my pixel scale of 1.36 Arc-Seconds, but it’s still not great. Fortunately, as the night progressed, that veil soon thinned out and dissipated, and was once again guiding at below 0.5″ Total RMS by 1AM. Did I mention how much I love this new mount?
The Cygnus wall can just about be seen in the middle of the single frame above, but bare in mind that the sky isn’t in complete darkness, and when shooting towards the east I’m shooting over the light polluted Black Country Conurbation. If I was shooting this same target in August, then it would be much higher and much darker, so hopefully the contrast will improve in subsequent sessions.
To help in this, I’m looking at investing in the IDAS NBZ filter, which is similar to the Optolong L-eXtreme filter. It has now established itself as being a superb dual narrowband filter for OSC (One Shot Colour) cameras, however it’s not without its faults. There’s slight differences between the two filters, most notably the passbands of the NBZ is slightly wider at 10nm for both Ha and O-III, instead of 7nm on the L-eXtreme. Hopefully that should be more lenient on my DSLR camera. The filter bands on the NBZ have also been pre-shifted to accommodate or fast optics, even down to F/2 like the Celestron RASA’s! Even at F/5 like my 130PDS, the L-eXtreme only allows 50% of the Hydrogen-Alpha to pass through, whereas the NBZ would allow more like 80%. Another positive is it’s par-focal with my current NGS1, so when I upgrade to a filter wheel, I can use the broadband to focus and then swap to the NBZ.
In the end though I managed to gather 29 light frames before nautical dawn occurred at 2:45AM, however I had to remove two frames due to badly shaped stars. Therefore, with the remaining 27 frames stacked together, giving me a total exposure of 2 hours 15 minutes on this stunning target.
This is a decent start to my summer project, however I only need 20 more clear nights to get the exposure time I envisage! It all depends though if I can afford the NBZ and then I start from scratch. I might just create a star mask from this broadband stack and use that to regain some natural star colour; I will just have to wait and see what happens in the coming months.
I’ve had to crop the image down a little bit, as the bright orange star on the left hand side of the single frame caused a halo artefact which could easily be seen, however this sets the focus on the wall instead, so not really a downside. The final image is a little grainy and noisy, but imaging in the summer plays havoc with thermal noise. Hopefully with more exposure time this should smoothen out to give a really detailed image as the final result!
Hopefully the clear weather stays around now for the summer, as I want to try and get out to more places and dark sky locations. I’ve got big plans coming this summer, so stay tuned for that!
Till next time, where ever you are, I wish you all clear skies!