The Collaborative International Dictionary of English v.0.48:

Emersion \E*mer"sion\, n. [Cf. F. ['e]mersion. See Emerge.]
   1. The act of emerging, or of rising out of anything; as,
      emersion from the sea; emersion from obscurity or
      difficulties.
      [1913 Webster]

            Their immersion into water and their emersion out of
            the same.                             --Knatchbull.
      [1913 Webster]

   2. (Astron.) The reappearance of a heavenly body after an
      eclipse or occultation; as, the emersion of the moon from
      the shadow of the earth; the emersion of a star from
      behind the moon.
      [1913 Webster]

WordNet (r) 3.0 (2006):

emersion
    n 1: (astronomy) the reappearance of a celestial body after an
         eclipse [syn: egress, emersion] [ant: immersion,
         ingress]
    2: the act of emerging [syn: emergence, emersion]