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