( ( In Astronomy ) ( , ( ( a nucleus ) ( ( is ( ( the center ) ( of ( ( ( ( the head ) ( of ( a comet ) ) ) or ) ( ( the ( ( ( central or ) brightest ) part ) ) ( of ( a ( ( nebula or ) galaxy ) ) ) ) ) ) ) ) . ) ) ) )
(ROOT (S (PP (IN In) (NP (NNP Astronomy))) (, ,) (NP (DT a) (NN nucleus)) (VP (VBZ is) (NP (NP (DT the) (NN center)) (PP (IN of) (NP (NP (NP (DT the) (NN head)) (PP (IN of) (NP (DT a) (NN comet)))) (CC or) (NP (NP (DT the) (ADJP (JJ central) (CC or) (JJ brightest)) (NN part)) (PP (IN of) (NP (DT a) (NN nebula) (CC or) (NN galaxy)))))))) (. .)))
In Astronomy, a nucleus is the center of the head of a comet or the central or brightest part of a nebula or galaxy .
(ROOT (S (NP (NP (DT The) (NN head)) (PP (IN of) (NP (DT the) (NN sperm)))) (VP (VBZ contains) (NP (DT the) (NN nucleus))) (. .)))
The head of the sperm contains the nucleus.