This was my first attempt at a star trails picture. I had the camera take 150 pictures at 20 seconds each, but somehow I only ended up with 76 photos. Don't know what went wrong, but I think the effect was still achieved. Then I stacked the images in Nik, on their HDR program. Turned out pretty good for my first try at it, I think.
I took this image tonight, still 99% of full (last night was the 100% supermoon). It's 8 images taken through my giant telescope with DSLR attached, then stitched together, then processed. I think it turned out pretty good: