I'm sure I've seen this phenomenon many times but until I saw it in one of my photography books I didn't pay any attention. It's called the "Belt of Venus" and it is the pink band above the horizon Just after sunset or just before sunrise.
With your back to the sunset (or sunrise) you see the light reflected off the atmosphere in the opposite direction of the setting or rising sun. The blue band below the pink is the earths shadow.
Tony Flanders at Sky and Telescope explains it much better than I can. Look for it the next time you have a clear sky at sunset or sunrise.
Check our SkyWatch Friday for more views of the sky.