You’ve seen waves in the water. But have you ever seen them in the sky? A photographer spotted these “waves” in December in Wyoming. They’re named Kelvin-Helmholtz clouds after two scientists who studied them in the 1800s. 

The clouds form when air moves over a high land feature, such as a hill. The air is pushed up as it travels over the hill. Then a force called gravity pulls the air back down. When this happens again and again, it can create the wave effect.