The Collaborative International Dictionary of English v.0.48:

Obscuration \Ob`scu*ra"tion\, n. [L. obscurativ: cf. F.
   obscuration. See Obscure, v. t. ]
   The act or operation of obscuring; the state of being
   obscured; as, the obscuration of the moon in an eclipse.
   --Sir J. Herschel.
   [1913 Webster]