( ( January 13 ) ( , ( ( 2000 ( February ( Planet ( Observing Session ) ) ) ) ( ( Because ( it ( 's ( so ( close ( to ( our Sun ) ) ) ) ) ) ) ( , ( Mercury ( ( is ( rarely ( visible ( to ( Earth-bound observers ) ) ) ) ) . ) ) ) ) ) ) )
(ROOT (S (NP (NNP January) (CD 13)) (, ,) (NP (CD 2000) (NNP February) (NNP Planet) (NNP Observing) (NN Session)) (SBAR (IN Because) (S (NP (PRP it)) (VP (VBZ 's) (ADJP (RB so) (JJ close) (PP (TO to) (NP (PRP$ our) (NN Sun))))))) (, ,) (NP (NNP Mercury)) (VP (VBZ is) (ADJP (RB rarely) (JJ visible) (PP (TO to) (NP (JJ Earth-bound) (NNS observers))))) (. .)))
January 13, 2000 February Planet Observing Session Because it's so close to our Sun, Mercury is rarely visible to Earth-bound observers.
(ROOT (S (NP (NNP Mercury)) (VP (VBZ is) (ADVP (RB always)) (ADJP (ADJP (JJR closer)) (PP (TO to) (NP (DT the) (NN sun)))) (SBAR (IN than) (S (NP (PRP it)) (VP (VBZ is) (PP (TO to) (NP (NN earth))))))) (. .)))
Mercury is always closer to the sun than it is to earth.