Photographing celebrity's heavenly body (8,4)
I believe the answer is:
shooting star
'heavenly body' is the definition.
(shooting star is a kind of heavenly body)
'photographing celebrity's' is the wordplay.
'photographing' becomes 'shooting' ('shoot' can be a synonym of 'photograph').
'celebrity's' becomes 'star' (I've seen this before).
'shooting'+'star'='SHOOTING STAR'
(Other definitions for shooting star that I've seen before include "on which you'd make a wish?" , "possibly a streaker?" , "fireball" , "One making meteoric progress" , "one that reaches meteoric heights?" .)