The space explorers study? (9)
I believe the answer is:
astronomy
'study?' is the definition.
(astronomy is a kind of study)
I cannot understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for astronomy that I've seen before include "Study of stars etc" , "Science that deals with celestial objects" , "Tory mason engaged in study of stars" , "Scientific study of heavenly bodies" , "Scientific study of the universe" .)