( ( ( For ( distances ( ( to ( ( other parts ) ( of ( the ( Milky ( Way Galaxy ) ) ) ) ) ) ( -LRB- ( ( or ( even further ) ) -RRB- ) ) ) ) ) ( , ( astronomers ( ( use ( ( units ( of ( ( ( ( ( the light-year ) or ) ( the parsec ) ) . ) ( ( The ( light-year ( we ( ( have already ) defined ) ) ) ) . ) ) ) ) ( ( The parsec ) ( ( is ( equal ( to ( 3.3 light-years ) ) ) ) . ) ) ) ) ( Using ( the light-year ) ) ) ) ) ) ( , ( we ( ( can ( say that ) ) : ) ) ) )
(ROOT (S (S (PP (IN For) (NP (NP (NNS distances)) (PP (PP (TO to) (NP (NP (JJ other) (NNS parts)) (PP (IN of) (NP (DT the) (NNP Milky) (NNP Way) (NNP Galaxy))))) (PRN (-LRB- -LRB-) (CC or) (FRAG (RB even) (ADVP (RB further))) (-RRB- -RRB-))))) (, ,) (NP (NNS astronomers)) (VP (VBP use) (NP (NP (NNS units)) (PP (IN of) (NP (NP (NP (DT the) (NN light-year)) (CC or) (NP (DT the) (NN parsec)) (. .)) (SBAR (FRAG (NP (DT The) (NN light-year) (SBAR (S (NP (PRP we)) (VP (VBP have) (ADVP (RB already)) (VP (VBN defined)))))) (. .))))) (SBAR (S (NP (DT The) (NN parsec)) (VP (VBZ is) (ADJP (JJ equal) (PP (TO to) (NP (CD 3.3) (NNS light-years))))) (. .)))) (S (VP (VBG Using) (NP (DT the) (NN light-year)))))) (, ,) (NP (PRP we)) (VP (MD can) (VP (VB say) (NP (DT that)))) (: :)))
For distances to other parts of the Milky Way Galaxy (or even further),  astronomers use units of the light-year or the parsec . The light-year we have already defined. The parsec is equal to 3.3  light-years.  Using the light-year, we can say that :
(ROOT (FRAG (S (S (VP (TO To) (VP (VB express) (NP (NP (DT the) (NN distance)) (PP (IN between) (NP (NP (DT the) (JJ milky) (NN way) (NN galaxy)) (CC and) (NP (JJ other) (NNS galaxies)))))))) (, ,) (NP (NP (DT the) (ADJP (RBS most) (JJ appropriate)) (NN unit)) (PP (IN of) (NP (NN measurement)))) (VP (VBZ is) (NP (DT the) (NN light-year))))))