Atmospheric phenomenon (6)
I believe the answer is:
aurora
'atmospheric phenomenon' is the definition.
(aurora is a kind of atmospheric phenomenon)
This is the entire clue.
(Other definitions for aurora that I've seen before include "Dawn goddess; polar lights" , "Roman Godess of the Dawn" , "7 ... borealis, ... lights" , "Display of lights in the night sky" , "Northern or southern lights" .)