( First ( , ( it ( ( was ( discovered ( that ( ( the Sun ) ( was ( ( the center ) ( of ( gravity ( of ( the ( Solar system ) ) ) ) ) ) ) ) ) ) ) ; ) ) ) )
(ROOT (S (ADVP (RB First)) (, ,) (NP (PRP it)) (VP (VBD was) (VP (VBN discovered) (SBAR (IN that) (S (NP (DT the) (NNP Sun)) (VP (VBD was) (NP (NP (DT the) (NN center)) (PP (IN of) (NP (NP (NN gravity)) (PP (IN of) (NP (DT the) (NNP Solar) (NN system))))))))))) (: ;)))
First, it was discovered that the Sun was the center of gravity of the Solar system;
(ROOT (S (NP (DT The) (NN sun)) (VP (VBZ is) (NP (NP (DT the) (NN center)) (PP (IN of) (NP (PRP$ our) (JJ solar) (NN system))))) (. .)))
The sun is the center of our solar system.