Astronomy Answers
From the Astronomical Dictionary


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The description of the word you requested from the astronomical dictionary is given below.

synodical

sunodos = [Greek] meeting; from sun = [Greek] together, and hodos = [Greek] road

A synodical period is the period after which the phases of a celestial body as seen from another celestial body repeat themselves. If only a single body is mentioned, then the synodical period as seen from Earth is usually meant.

After a synodical month, the Moon has reached the same phase again (for example: full moon). The time between two oppositions or (similar) conjunctions of a planet is the synodical period of the planet. After that time, the Earth has caught up again with the planet (or the planet with the Earth) in its orbit around the Sun. The time after which a certain sunspot returns to the same location on the solar disk is the synodical period of the Sun (but that is not the same everywhere on the Sun, because of differential rotation).

The synodical periods of the planets are, rounded to whole days: Mercury 116, Venus 584, Mars 780, Jupiter 399, Saturn 378, Uranus 370, Neptune 367, Pluto (at present) 367. Calculate it yourself.

Periods of motion measured relative to the stars are called sidereal periods.