#nucleus.midpoint__nucleu  (astronomy) the center of the head of a comet; consists of small solid particles of ice and frozen gas that vaporizes on approaching the sun to form the coma and tail
  supertype:  midpoint__center__centre  a point equidistant from the ends of a line or the extremities of a figure
  part of:  comet  (astronomy) a relatively small extraterrestrial body consisting of a frozen mass that travels around the sun in a highly elliptical orbit

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