( ( To ( understand ( our ( changing seasons ) ) ) ) ( , ( ( ( ( follow ( ( Earth 's ) path ) ) ( around ( ( the sun ) ( for one ) ) ) ) ( ( complete orbit ) ( -LRB- ( ( ( i.e. , ) ( one year ) ) -RRB- ) ) ) ) . ) ) )
(ROOT (SINV (S (VP (TO To) (VP (VB understand) (NP (PRP$ our) (VBG changing) (NNS seasons))))) (, ,) (VP (VBP follow) (NP (NP (NNP Earth) (POS 's)) (NN path)) (PP (IN around) (NP (NP (DT the) (NN sun)) (PP (IN for) (NP (CD one)))))) (NP (NP (JJ complete) (NN orbit)) (PRN (-LRB- -LRB-) (NP (NNP i.e.)) (, ,) (NP (CD one) (NN year)) (-RRB- -RRB-))) (. .)))
To understand our changing seasons, follow Earth's path around the sun for one complete orbit (i.e., one year).
(ROOT (S (NP (PRP It)) (VP (VBZ takes) (PP (IN about) (NP (NP (CD one) (NN year)) (PP (IN for) (NP (NN earth))))) (S (VP (TO to) (VP (VB orbit) (NP (DT the) (NN sun)))))) (. .)))
It takes about one year for earth to orbit the sun.