Solar halo (6)
I believe the answer is:
corona
'solar halo' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for corona that I've seen before include "Part of the sun's atmosphere visible during a total eclipse" , "shining circle" , "Circle of light around sun or moon" , "A glow of light around something" , "Aureole" .)