( ( When ( summer ( occurs ( in ( a hemisphere ) ) ) ) ) ( , ( it ( ( ( ( is ( due ( to ( that hemisphere ) ) ) ) ( receiving ( ( more ( direct rays ) ) ( of ( ( the sun ) ( than ( the ( opposite hemisphere ) ) ) ) ) ) ) ) ( where ( it ( is winter ) ) ) ) . ) ) ) )
(ROOT (S (SBAR (WHADVP (WRB When)) (S (NP (NN summer)) (VP (VBZ occurs) (PP (IN in) (NP (DT a) (NN hemisphere)))))) (, ,) (NP (PRP it)) (VP (VBZ is) (ADJP (JJ due) (WHPP (TO to) (WHNP (WDT that) (NN hemisphere)))) (S (VP (VBG receiving) (NP (NP (JJR more) (JJ direct) (NNS rays)) (PP (IN of) (NP (NP (DT the) (NN sun)) (PP (IN than) (NP (DT the) (JJ opposite) (NN hemisphere)))))))) (SBAR (WHADVP (WRB where)) (S (NP (PRP it)) (VP (VBZ is) (NP (NN winter)))))) (. .)))
When summer occurs in a hemisphere, it is due to that hemisphere receiving more direct rays of the sun than the opposite hemisphere where it is winter.
(ROOT (S (NP (NP (DT The) (NN tilt)) (PP (IN of) (NP (NP (NN earth)) (PP (IN on) (NP (PRP$ its) (NNS axis)))))) (VP (VBZ causes) (NP (NN summer)) (S (VP (TO to) (VP (VB be) (VP (VBN warmer) (PP (IN than) (NP (NP (NN winter)) (PP (IN in) (NP (DT the) (JJ northern) (NN hemisphere))))) (SBAR (IN because) (S (NP (NP (DT the) (NNS rays)) (PP (IN of) (NP (DT the) (NN sun)))) (VP (VBP strike) (NP (DT the) (JJ northern) (NN hemisphere)) (ADVP (ADVP (RBR more) (RB directly)) (PP (IN in) (NP (DT the) (NN summer)))))))))))) (. .)))