Light bending or going in straight lines? The question of optics on a cold day.

Very cold today. When I got up at 7 it was -24, but when I was going to work at 9, it was -27. There were sun dogs around the sun, an indicator of extreme cold. In class today, Geremy came in to talk about a range of old 19th century devices. We blanked out the door and built a camera obscura into the classroom. Some people didn't quite understand the optic rule where things are turned upside down because light moves in straight lines. Of course, the nature of light outside in our sky is proof that light bends. Hmm.