Extraordinarily remote heavenly body (6)
I believe the answer is:
meteor
'heavenly body' is the definition.
(meteor is a kind of heavenly body)
'extraordinarily remote' is the wordplay.
'extraordinarily' is an anagram indicator (I've seen this in other clues).
'remote' anagrammed gives 'METEOR'.
(Other definitions for meteor that I've seen before include "It causes a streak of light in the night sky" , "it appears as a streak of light" , "fighter" , "Small extraterrestrial body" , "Remote (anag)" .)