( ( An age ) ( ( ( is ( the time ) ) ( that ( it ( ( ( takes ( ( the ( Earth 's ) ) axis ) ) ( to precess ) ) ( through ( ( one sign ) ( of ( the zodiac ) ) ) ) ) ) ) ) . ) )
(ROOT (S (NP (DT An) (NN age)) (VP (VBZ is) (NP (DT the) (NN time)) (SBAR (IN that) (S (NP (PRP it)) (VP (VBZ takes) (NP (NP (DT the) (NN Earth) (POS 's)) (NNS axis)) (PP (TO to) (NP (NNS precess))) (PP (IN through) (NP (NP (CD one) (NN sign)) (PP (IN of) (NP (DT the) (NN zodiac))))))))) (. .)))
An age is the time that it takes the Earth's axis to precess through one sign of the zodiac.
(ROOT (S (NP (PRP It)) (VP (VBZ takes) (NP (NN earth) (CD one) (NN week)) (S (VP (TO to) (VP (VB rotate) (PP (IN on) (NP (PRP$ its) (NNS axis))) (NP (CD seven) (NNS times)))))) (. .)))