Ultra-rare 'rainbow clouds' light up the Arctic Circle like auroras in stunning new photos

Rare clouds that give off bright, multi-colored light like an aurora were recently spotted at multiple locations in the Arctic. But what causes them?

Ultra-rare 'rainbow clouds' light up the Arctic Circle like auroras in stunning new photos
Rare clouds that give off bright, multi-colored light like an aurora were recently spotted at multiple locations in the Arctic. But what causes them?