Celestial event (7)
I believe the answer is:
eclipse
'celestial event' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for eclipse that I've seen before include "Dominate - put in the shade" , "Celestial phenomenon" , "Heavenly phenomenon" , "The obscuring of one celestial body by another" , "Over-shadow as the earth may the moon" .)