( ( A galaxy ) ( ( is ( ( a ( vast island ) ) ( of ( hundreds ( of ( billions ( of ( ( ( ( ( stars ( -LRB- ( ( solar systems ) -RRB- ) ) ) , ) nebulas ) and ) ( star clusters ) ) ) ) ) ) ) ) ) . ) )
(ROOT (S (NP (DT A) (NN galaxy)) (VP (VBZ is) (NP (NP (DT a) (JJ vast) (NN island)) (PP (IN of) (NP (NP (NNS hundreds)) (PP (IN of) (NP (NP (NNS billions)) (PP (IN of) (NP (NP (NNS stars)) (PRN (-LRB- -LRB-) (NP (JJ solar) (NNS systems)) (-RRB- -RRB-)) (, ,) (NP (NNS nebulas)) (CC and) (NP (NN star) (NNS clusters)))))))))) (. .)))
A galaxy is a vast island of hundreds of billions of stars (solar systems), nebulas and star clusters.
(ROOT (S (NP (DT A) (NN galaxy)) (VP (VBZ is) (VP (RBS best) (VBN described) (PP (IN as) (NP (NP (DT a) (NN cluster)) (PP (IN of) (NP (NP (NNS billions)) (PP (IN of) (NP (NNS stars))))))))) (. .)))