Ice crystals are also responsible for some interesting phenomena in the sky. I frequently see sundogs in the sky, which I'm told are formed by sunlight being refracted by ice crystals in the clouds. Here are a pair of sundogs I saw one day last week. I think the second (to the left of the sun) is probably in the cloud of a jet contrail. Even on otherwise clear days, we are likely to have some jet trails in the sky here, so there is plenty of opportunity to see sundogs.