An image believed to be that of a hole-punch cloud. Scientists say airplanes create these patterns when they fly through certain types of clouds. The water in the clouds can turn to rain or snow and fall to the ground. H. Raab/Vesta/Wikimedia Commons hide caption

itoggle caption H. Raab/Vesta/Wikimedia Commons

A demonstrator uses a slingshot during a protest against a planned high-speed rail line running through the Susa valley in Chiomonte, northern Italy. STR/AFP/Getty Images hide caption

itoggle caption STR/AFP/Getty Images

Bob Carter, group vice president and general manager, Toyota Division, introduces the Prius v midsize hybrid-electric vehicle (left) and the Prius C Concept vehicle at the North American International Auto Show in Detroit on Jan. 10. Paul Sancya/AP hide caption

itoggle caption Paul Sancya/AP

An environmental clean water protester participates in a rally at the Pennsylvania state capitol in Harrisburg against the drilling of the Marcellus Shale natural gas formation. Bradley C. Bower/AP hide caption

itoggle caption Bradley C. Bower/AP