planisphere (n.)

"map of the heavens made by projection of a portion of the celestial sphere onto a plane surface," late 14c., planisperie, from Anglo-Latin planispherium, Medieval Latin planisphaerium, from Latin planus "flat, level" (from PIE root *pele- (2) "flat; to spread") + sphaera (see sphere (n.)). Related: Planispheric.