Shiranui (optical phenomenon)

Shiranui (不知火, unknown fire; Shiranuhi in the historical kana orthography) is an atmospheric ghost light told about in Kyushu. They are said to appear on days of the noon moon such as the kaijitsu (29th or 30th day) of the seventh month of the lunisolar Japanese calendar when the wind is weak, in the Yatsushiro Sea and the Ariake Sea.