Sun Circle
Seen from Hai Duong, Vietnam, the bright sun sports a rainbow-colored halo in a picture taken September 17.
The circle of color is an optical effect created as ice crystals in high-altitude clouds refract, or bend, light. Because the upper reaches of Earth’s atmosphere are almost always below freezing, sun halos and related phenomena—such as sun dogs and pillars—can be seen year-round, according to NASA.
Photograph by Tho Le Duc via National Geographic