( ( Nobody quite ) ( ( knows ( why ( it ( ( ( 's ( so hot ) ) , ) ( when ( ( ( the ( Sun 's ) ) surface ) ( is ( much cooler ) ) ) ) ) ) ) ) . ) )
(ROOT (S (NP (NN Nobody) (RB quite)) (VP (VBZ knows) (SBAR (WHADVP (WRB why)) (S (NP (PRP it)) (VP (VBZ 's) (ADJP (RB so) (JJ hot)) (, ,) (SBAR (WHADVP (WRB when)) (S (NP (NP (DT the) (NNP Sun) (POS 's)) (NN surface)) (VP (VBZ is) (ADJP (RB much) (JJ cooler))))))))) (. .)))
Nobody quite knows why it's so hot, when the Sun's surface is much cooler.
(ROOT (S (NP (NP (DT The) (NN surface)) (PP (IN of) (NP (DT the) (NN sun)))) (VP (VBZ is) (ADJP (RB much) (JJ hotter) (PP (IN than) (NP (NP (RB almost) (NN anything)) (PP (IN on) (NP (NN earth))))))) (. .)))