They learn of the sun's trapping carbon and hydrogen (8)
I believe the answer is:
scholars
'they learn' is the definition.
The definition suggests an adverb but the answer is not.
'the sun's trapping carbon and hydrogen' is the wordplay.
'the sun's' becomes 'solars' (I am not sure about this - if you are sure you should believe this answer much more).
'trapping' means one lot of letters goes inside another.
'carbon' becomes 'c' (C is the chemical symbol for carbon).
'and' is a charade indicator (letters next to each other).
'hydrogen' becomes 'h' (H is the chemical symbol for hydrogen).
'c'+'h'='ch'
'solars' placed around 'ch' is 'SCHOLARS'.
'of' is the link.
Can you help me to learn more?
(Other definitions for scholars that I've seen before include "Learned people who have studied long" , "Pupils or learned people" , "They study" , "Very learned persons" , "Cross Hal mixed with pupils" .)