Image of sun is captured in revolutionary data storage medium (4)
I believe the answer is:
disc
'image of sun' is the definition.
(disc can mean an image of the sun or moon)
'is captured in revolutionary data storage medium' is the wordplay.
'captured in' is an insertion indicator.
'revolutionary' shows that the letters should be reversed in order (letters revolve around).
'data storage medium' becomes 'CD' (compact disc).
'cd' back-to-front is 'dc'.
'is' placed into 'dc' is 'DISC'.
(Other definitions for disc that I've seen before include "Forty-five" , "Record, CD" , "jockey may be after" , "put on by jockey?" , "Flat thin round object" .)