So, I got into a very quick discussion with a guy about star trail photography (multishot versus single long exposure). I championed the single, long exposure (like the film days) while he told me that that was impossible because of the full moon he was shooting in (nothing would show up was how I interpreted it). Anyway, I set out to prove a point by shooting under a 95% full moon and in a small city. I got my start trails, and a really weird red band down the side of the frame.
The red side was on the left. The temperature was about 55-60 F (the low for the night was 55 F). I was using a well used d300, ISO was 100, at f/22, with the 18-200mm set to 18mm, exposure was about 37 minutes.
Here is the RAW:
Here it is with the white balance corrected, the contrast dropped to 0, and brightened a bit:
I know there is a spot on the lens (trust me, it's the lens). Also, this red showed up in another 30+ exposure that I didn't like with the exact same pattern (moving the camera and rotating it a bit did not alter the angle of the pattern). It does not show up using normal exposures.
I've heard of hotspots appearing with long exposures but not a whole gradient.