Scientific study of heavenly bodies (9)
I believe the answer is:
astronomy
'scientific study of heavenly bodies' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for astronomy that I've seen before include "Scientific interest" , "Scientific study of stars and planets" , "Scientific study of the universe" , "Tory moans (anag.)" , "Stargazing" .)