Lenticular clouds are spectacular natural formations that appear at high altitudes, usually above mountains. They are lens-shaped clouds often mistaken for UFOs or flying saucers, due to their unique appearance. They take form as a current of moist air is forced to pass above a mountain. In this situation the moist air condenses and generates a lenticular cloud.
Famous photos of lenticular clouds include Mount Fuji and Mount Shasta. In case you are a passionate photographer in search for such a phenomenon, you may just run into one while being around tall hills or mountain tops. In the mean time, have fun going through the pictures.