Short version: Is there any physical reason why a sunset should look different than a sunrise? The only differences between the two situations that I can think of is that the atmosphere should be cooler during a sunrise than a sunset. There's also the accumulated smog consideration if you're near a city, i.e. there will be very little smog at sunrise vs quite a bit at sunset. Long version: I was just looking at a nice coastline picture and trying to figure out whether it was a sunset on an easterly facing coast or sunrise on a westernly facing coast when it occured to me that the two situations should be roughly symmetric and so you shouldn't be able to tell the difference. I commented on this to a friend of mine, intending to get a chuckle out of sharing the experience, when he said that you can tell the difference by the colors in the sky. Now my friend isn't a physicist (or a meteorologist, for that matter), but he does do a lot of backpacking and has seen his fair share of sunrises and sunsets so there's a good chance he knows what he's talking about. I haven't been able to convince myself that there would be any real difference between the two though.