As a callous young man, I’d visit Shiranui (不知火 - literally, “don’t know fire”), a small town on the eastern side of the Uto Peninsula,, pull out my lighter, and say, “Look! Fire!” It was only recently I learned the depth of my ignorance.
Similar to the mirages common in the deserts of my native California, the phenomenon is an optical illusion in which the heat exuded from exposed mud flats at low tide confront cooler air above, causing reflected lights from Yatsushiro and boats on the sea to appear to float untethered - hence, the name would be better translated as “mysterious fire.” The cause of this phenomenon went unknown until the early 20th c., so it’s no wonder people marveled at it for centuries. Unfortunately, the dredging of the mudflats has drastically reduced the frequency of the phenomenon, but it lives on in yokai. - William