An Etymological Dictionary of Astronomy and Astrophysics
English-French-Persian

Of or pertaining to the → conjunction of two or more heavenly bodies, especially the interval between two successive conjunctions of a planet or the Moon with the Sun.

From L.L. synodicus, from Gk. synodikos, from synodos "assembly, meeting," from → syn- "together" + hodos "a going, a way."

Hamâgam, literally "coming together," from ham-, → syn- "together," + -â- epenthetic vowel + gam from O.Pers. gam- "to come; to go," Av. gam- "to come; to go," jamaiti "goes," Mod.Pers. âmadan "to come," gâm "step, pace;" cf. Skt. gamati "goes;" Gk. bainein "to go, walk, step;" L. venire "to come;" Tocharian A käm- "to come;" O.H.G. queman "to come;" E. come; PIE stem *gwem- "to go, come."

The interval of 29.530 588 days (29d 12h 44m 2.80s), on average, between two successive → new Moons. Same as → lunation.

→ synodic; → month.

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.