( It ( ( ( is ( during ( this time ) ) ) ( that ( ( the star ) ( begins ( to ( ( ( run out ) ( of hydrogen ) ) ( so ( ( the star ) ( will ( ( ( ( lose ( its brightness ) ) and ) also ) ( contract ( in size ) ) ) ) ) ) ) ) ) ) ) ) . ) )
(ROOT (S (NP (PRP It)) (VP (VBZ is) (PP (IN during) (NP (DT this) (NN time))) (SBAR (IN that) (S (NP (DT the) (NN star)) (VP (VBZ begins) (S (VP (TO to) (VP (VB run) (PRT (RP out)) (PP (IN of) (NP (NN hydrogen))) (SBAR (IN so) (S (NP (DT the) (NN star)) (VP (MD will) (VP (VP (VB lose) (NP (PRP$ its) (NNS brightness))) (CC and) (ADVP (RB also)) (VP (VB contract) (PP (IN in) (NP (NN size))))))))))))))) (. .)))
It is during this time that the star begins to run out of hydrogen so the star will lose its brightness and also contract in size.
(ROOT (S (SBAR (WHADVP (WRB When)) (S (NP (NP (DT the) (NN core)) (PP (IN of) (NP (DT a) (NN star)))) (VP (VBZ begins) (S (VP (TO to) (VP (VB run) (ADJP (JJ low)) (PP (IN on) (NP (NN hydrogen))))))))) (, ,) (NP (PRP it)) (VP (VBZ contracts)) (. .)))