The study of the stars and planets (9)
I believe the answer is:
astronomy
'the study of the stars and planets' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for astronomy that I've seen before include "Study of stars etc" , "Mayors not involved in study of the stars" , "Scientific study of heavenly bodies" , "The study of celestial bodies" , "Stargazing" .)