Ring around sun - (around, encircling or above surface of) (6)
I believe the answer is:
corona
'ring around sun' is the definition.
(astronomical term)
'around encircling or above surface of' is the wordplay.
'around' becomes 'ca' (circa).
'encircling' is an insertion indicator.
'above surface of' becomes 'on'.
'or'+'on'='oron'
'ca' going around 'oron' is 'CORONA'.
(Other definitions for corona that I've seen before include "Ring round the sun or moon" , "fiery halo" , "Outer halo of the sun" , "Aureole" , "Crown; coloured ring" .)