Circumhorizon Arc Above Beijing, China

February 03, 2016

ChinaCHAIMG_2018 (2)

Photographer: Qian Zheng Rong
Summary Authors: Qian Zheng Rong; Jim Foster
Shown above in an otherwise gray, hazy sky is a lively strip of color known as a circumhorizon arc (CHA). It was observed from Beijing, China, around 11:30 a.m. on May 29, 2015. These colorful arcs form when sunlight is refracted through similarly-oriented, hexagonal ice crystals in cirrus clouds. To see CHAs, the Sun must be high in the spring and summer sky, as they can't be seen if the Sun is lower than 58 degrees above the horizon. Thus, in the mid-latitudes of the Northern Hemisphere, they're viewed only from about mid-May to mid-August. After this picture had been snapped, haze and pollution restricted the CHA's visibility, however, at approximately 1 p.m. an impressive 22 degree halo formed above the CHA.
Photo Details: Camera Maker: Apple; Camera Model: iPhone 4S; Focal Length: 4.3mm (35mm equivalent: 35mm); Aperture: ƒ/2.4; Exposure Time: 0.0001 s (1/7937); ISO equiv: 50.