An Etymological Dictionary of Astronomy and Astrophysics
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For planets, the mean interval of time between two successive → conjunctions with or → oppositions to the Sun. For example, → Mars has a synodic period of 779.9 days from Earth; thus Mars' oppositions occur once roughly 2.135 years. In comparison, the synodic period of → Venus is 583.9 days. If the sideral periods of the two bodies around the third are denoted T₁ and T₂, their synodic period is given by: 1/T_syn = |1/T₁ - 1/T₂|.

→ synodic; → period.