Experts in it will tell you if a stray moon is about (9)
I believe the answer is:
astronomy
'experts in it will tell you' is the definition.
I can't judge whether this defines the answer.
'a stray moon is about' is the wordplay.
'is about' indicates anagramming the letters.
'stray'+'moon'='straymoon'
'straymoon' with letters rearranged gives 'ASTRONOMY'.
'if' is the link.
Can you help me to learn more?
(Other definitions for astronomy that I've seen before include "Stargazing" , "Study of stars etc" , "Scientific study of stars and planets" , "Scientific study of heavenly bodies" , "Science that deals with celestial objects" .)