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| A circumzenithal arc forms in the sky above Huangpu district Monday morning. Photos: Courtesy of Shirley Han |
A circumzenithal arc, an optical phenomenon that looks like an inverted rainbow, appeared in the sky over Xuhui district around 8:20 am Monday morning.
Some of the people who spotted the phenomenon posted photos of what they called the "smiling rainbow" on their microblogs.
However, the phenomenon is something different than a rainbow, said Fu Yi, a press officer with the Shanghai Meteorological Bureau.
A circumzenithal arc can appear when sunlight passes through ice crystals that form 6,000 to 8,000 meters off the ground, creating a thin haze, according to the Shanghai Meteorological Bureau's website.
The ice crystals, which are smaller than grains of salt, serve as a prism for the light that forms the phenomenon, Fu said. The arc followed the appearance of a sun dog - another optical phenomenon in which two bright spots appear on either side of the sun.
"These are rare sights that do not occur regularly. People can only see them under specific conditions," Fu told the Global Times.
The phenomena can occur anywhere in the world at any time, but they are more common farther north, Fu added.
The circumzenithal arc remained for about an hour and then disappeared around 9:30 am, Fu said. The sun dog, which is also born from sunlight passing through ice crystals, garnered less attention because it only lasted a short time.
Cumquat market in S China's Guangxi
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