On Nov. 17, 1882, something odd appeared in the sky over Europe. The “strange celestial visitor” appeared low in the northeastern sky and elongated as it moved steadily from east to west over the course of two minutes. It was whitish or greenish-white, about 30 degrees long and 3 degrees wide, and had distinct edges.

Whatever it was, the thing was witnessed by professional astronomers across the continent and described in journals including Nature and The Observatory. Edward Walter Maunder of the Greenwich Royal Observatory said it moved “as the Sun, Moon, stars and planets move but nearly a thousand times as quickly.” Even 34 years later Maunder recalled the phenomenon as “unlike any other celestial object that I have ever seen. The quality of its light, and its occurrence while a great magnetic storm and a bright aurora were in progress, seem to establish its auroral origin. But it differed very widely in appearance from any other aurora that I have ever seen.”

What was it? No one knows.