Photo shows a moon hanging vertically above "Chumi Cave" in Zhaoqing City, south China's Guangdong Province on Dec. 22. (photo by Huang Yaohui, China News Agency)
The appearance of this rare phenomenon has three preconditions: there must be a full moon, it must occur during the winter solstice and the moon must reach 23.08 degrees north latitude, an expert said.The expert also said the next time it will be possible to observe this phenomenon will be 19 years later. In this century, we can only observe it six times.An expert shows the "Chumi Cave" on a map. The moon hung vertically above a cave, shining light inside on Dec. 22, the Winter Solstice.(photo by Huang Yaohui, China News Agency)