( ( By comparison ) ( , ( ( the earth ) ( ( ( ( rotates ( on ( ( its axis ) ( once ( per day ) ) ) ) ) and ) ( ( revolves around ) ( ( the sun ) ( once ( per year ) ) ) ) ) . ) ) ) )
(ROOT (S (PP (IN By) (NP (NN comparison))) (, ,) (NP (DT the) (NN earth)) (VP (VP (VBZ rotates) (PP (IN on) (NP (NP (PRP$ its) (NNS axis)) (PP (ADVP (RB once)) (IN per) (NP (NN day)))))) (CC and) (VP (VBZ revolves) (PRT (RP around)) (NP (NP (DT the) (NN sun)) (PP (ADVP (RB once)) (IN per) (NP (NN year)))))) (. .)))
By comparison, the earth rotates on its axis once per day and revolves around the sun once per year.
(ROOT (S (NP (NNP Earth)) (VP (VBZ rotates) (PP (PP (IN on) (NP (PRP$ its) (NNS axis)) (ADVP (RB once))) (CC times) (PP (IN in) (NP (CD one) (NN day))))) (. .)))