Exclamation of surprise on getting a vision during eclipse (6)
I believe the answer is:
corona
'vision during eclipse' is the definition.
(atmosphere of the Sun seen in an eclipse)
'exclamation of surprise on getting a' is the wordplay.
'exclamation of surprise' becomes 'cor' (expression of surprise).
'getting' is a charade indicator (letters next to each other).
'cor'+'on'+'a'='CORONA'
(Other definitions for corona that I've seen before include "Crown; coloured ring" , "Trumpet" , "Long cigar" , "Circle of light around sun or moon" , "fiery halo" .)