Watch out for planes!
The picture above was from my first set of experiments at night photography. I was pleased with the subtle gradient of the background (city glow), dotted with a few stars. I was less than pleased to realise that a passing plane had left its mark (bottom right).
In this case, I was just experimenting for the overall settings and wanted to view the picture full size on my computer before making any decisions but I think I will try again with a similar setup and, this time, see if I can avoid any planes passing by.
Wulf
ps. ... and, yes, the horizon of the picture is wonky - that is a side effect of the slightly dodgy tripod I was using rather than a lesson in after-dark photography.