Staring at twinkling heavenly body (5,4)
I believe the answer is:
giant star
'heavenly body' is the definition.
(giant star is a kind of heavenly body)
'staring at twinkling' is the wordplay.
'twinkling' indicates anagramming the letters.
'staring'+'at'='staringat'
'staringat' with letters rearranged gives 'GIANT STAR'.
(Other definitions for giant star that I've seen before include "big shiner" , "great luminary" , "heavenly body" .)