Threading the needle: SH2-90 + ISS - 09/07/2024
Hello again!
I admit, I'm not the best at consistently posting my pictures to the blog 😅 I am hoping to get more consistent with this though (wanna work thru the backlog of pictures to process and to post soon, been making progress on the processing part at least!), and I really want to set up a proper website for the blog as well!
For now, enjoy this picture of the International Space Station (ISS) transitting in front of the Sharpless2-90 HII Region (SH2-90) back at the start of summer last year!
I don't remember if I just wanted to take a crack at the ISS, or if I was looking for a deepsky target in Stellarium, but either way - I've noticed the ISS transitting a nebula while browsing around the sky, and I just HAD to give it a go!
Now, when I took my telescope out and set up.. I realized a problem! I didn't set the location in Stellarium on my PC properly, and the ISS was showing up offset from what I had planned earlier when checking the mobile version of the sky map which did have the correct location.. thankfully however I did manage to find another nebula - the SH2-90 - that ISS was actually gonna transit that night, so plans weren't lost!
I first targetted the area in question by plate solving images with from the DSLR (I did not have GOTO or guiding yet at that time..) and manually adjusting until I was in the right spot. The nebula of course wasn't coming thru in single subs on the unmodified DSLR, other than astrometry.net (to which I was very new at the time and didn't really know how to use properly yet) I relied on apparent star shapes to get the framing roughly how I wanted. This process took a while, and in the meantime I saw an earlier pass of the ISS in the sky, which meant I had about 90 minutes left to get on target before the pass I was interested in was gonna take place.
Once I was fairly confident I was roughly on target, I switched out the camera for the 462mm, took a few second long exposure to get the stars and verified by looking at the star patterns in stellarium vs in the image (as well as platesolving I believe? not sure, it has been a while since then haha) that I was right on target, making the necessary adjustments. I was done with targetting with just a moment to spare before the ISS started flying overhead, cutting it quite close! But of course I wouldn't be certain I got it right until I saw the station zap by on my laptop's screen.. Shortly before the transit, I started recording with SharpCap, and thankfully I managed to nail the framing on the transit! (not easy to manually aim a 462mm at 1200mm focal lenght with just the adjustment knobs!) Then I took a few second long exposure to get the stars for star alignment later when compositing. Then I switched back to the DSLR and imaged for the rest of the night.
The nebula part was processed separately in Siril, utilizing StarNet for independent starless processing. The data wasn't the greatest (one of my first images after a several-years-long hiatus from the hobby, and I didn't get far the previous time haha) but I'm happy with how much I was able to squeeze out of it. The general process was done a while ago, but just before uploading I have ran it thru DeepSNR in PixInsight to make it a bit nicer.
The recorded frames for the ISS were extracted using PIPP, then combined in Paint.NET (adding each frame as a layer, and taking a slice from each imposed on the previous one, to get the ISS from each frame all in one image). Then I used the slightly longer exposure 462mm image with stars to align the framing on top of the deepsky picture based on the stars. Then the aligned combined ISS image was added as a layer with Additive blend mode on top of the deepsky image, achieving the final composition.
(I also realized now that combining the ISS frames using additive blender would have been a cleaner and better solution, well it has been a few months since I took this haha)
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