Synodic Period - Encyclopedia Britannica 1911

GEOGRAPHICAL NAMES

SYNODIC PERIOD, in astronomy, the apparent period of a planet or satellite when its revolution is referred to the line passing through the earth or the sun. In the case of the planets it is the period between successive conjunctions of the same kind, inferior or superior, with the sun. In the case of the satellites it is the period relative to the radius vector from the sun.