Though sun halos can happen year-round, they are especially noticeable in the winter when ice-filled cirrus clouds are more common.

Halos can form around both the sun and the moon, but stars are not bright enough to produce a halo effect. They form when tiny ice crystals refract and reflect the light in an organized way.

Hong Kong on Tuesday witnessed a rare natural phenomenon, a halo around the sun, that can be experienced only when meteorological conditions are right. The Observatory posted pictures on its ...