( ( ( An Introduction ) ( The ( western calendar ) ) ) ( ( is ( based ( on ( ( ( the sun ) , ) ( ( in which ) ( ( a year ) ( is ( ( the time ) ( ( required ( for ( the earth ) ) ) ( to ( complete ( ( one orbit ) ( around ( the sun ) ) ) ) ) ) ) ) ) ) ) ) ) ) . ) )
(ROOT (S (NP (NP (DT An) (NNP Introduction)) (NP (DT The) (JJ western) (NN calendar))) (VP (VBZ is) (VP (VBN based) (PP (IN on) (NP (NP (DT the) (NN sun)) (, ,) (SBAR (WHPP (IN in) (WHNP (WDT which))) (S (NP (DT a) (NN year)) (VP (VBZ is) (NP (NP (DT the) (NN time)) (VP (VBN required) (PP (IN for) (NP (DT the) (NN earth))) (S (VP (TO to) (VP (VB complete) (NP (NP (CD one) (NN orbit)) (PP (IN around) (NP (DT the) (NN sun)))))))))))))))) (. .)))
An Introduction The western calendar is based on the sun, in which a year is the time required for the earth to complete one orbit around the sun.
(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.