A circular rainbow was spotted in downtown Shanghai and neighboring cities at around 8:00 on Monday morning, and pictures of the natural phenomenon have circulated widely on the Internet, cheering up local morning commuters. Local meteorologists explained that the sight was actually an optical phenomenon known as a circumzenithal arc or Bravais arc, caused by refraction of sunlight through horizontally oriented ice crystals. They said these crystals are part of cirrus clouds that hang about 15 kilometers above the ground. This type of rainbow is rarely seen as it occurs so high in the sky and usually in frigid areas in the north. Photo: IC