On the left is the remains of the sunset and on the right the light pollution of Cheyenne, Wyoming.
Note: to do this yourself, make sure to begin just after dark. Our eyes may not see it, but these sunset colors are still around at that time. Next be sure to use as high of ISO as you can get away with for a 30 sec. exposure while maintaining low noise. Finally put on a fast lens and shoot wide open or near it. For this one I shot it on a 17-35 f/2.8 @ 17mm, F4 for 30 seconds at 800 ISO. I would think shooting a 1.4 or 1.8 lens wide open might work even better for keeping the exposure time needed down.