Somehow pro-Venus wanting a light in the heavens (9)
I believe the answer is:
supernova
'light in the heavens' is the definition.
(exploding star)
'somehow pro-venus wanting a' is the wordplay.
'somehow' indicates an anagram.
'wanting' says to put letters next to each other.
'pro'+'venus'='provenus'
'provenus' with letters rearranged gives 'supernov'.
'supernov'+'a'='SUPERNOVA'
(Other definitions for supernova that I've seen before include "cosmic explosion" , "Exploding star that becomes much brighter" , "Exploding star that becomes extremely luminous" , "Star made brilliant by stellar explosion" , "Star in decline" .)