"Massive auroras and an unidentified object are dancing in the sky above Abisko National Park," reports Chad Blakley of Abisko, Sweden. "Our group of eight lucky aurora watchers were out in the park enjoying the display when something very odd appeared in the sky - a luminous crescent-shaped cloud with what appears to be some sort of a flowing, cloud like tail." The park's webcam captured this image of the cloud:
Aurora and Mystery Cloud
© Chad Blakley
Taken by Chad Blakley on November 11, 2016 @ Abisko National Park, Sweden.
"At first I thought the object was lens flare produced by the bright Moon, but the object has moved from one area of the sky to another in four sequential photographs captured over a 20 minute timeframe," adds Blakley. "Seeing this incredible phenomenon share the sky with strong auroras has truly been a once in a lifetime event for our guests."

The cloud resembles a rocket fuel dump. Readers, if you think you know what this is, tell us.