( ( Lunar eclipses ) ( ( occur ( when ( ( the Moon ) ( passes ( through ( ( the ( Earth 's ) ) shadow ) ) ) ) ) ) . ) )
(ROOT (S (NP (NNP Lunar) (NNS eclipses)) (VP (VBP occur) (SBAR (WHADVP (WRB when)) (S (NP (DT the) (NNP Moon)) (VP (VBZ passes) (PP (IN through) (NP (NP (DT the) (NN Earth) (POS 's)) (NN shadow))))))) (. .)))
Lunar eclipses occur when the Moon passes through the Earth's shadow.
(ROOT (S (SBAR (WHADVP (WRB When)) (S (NP (NP (NN earth) (POS 's)) (NN shadow)) (VP (VBZ falls) (PP (IN on) (NP (DT the) (NN moon)))))) (, ,) (NP (DT the) (NN shadow)) (VP (VBZ causes) (NP (DT a) (NN lunar) (NN eclipse))) (. .)))
When earth’s shadow falls on the moon, the shadow causes a lunar eclipse.