会かい合ごう周しゅう期き

noun

synodic period

Astronomical term for the time it takes a celestial body to return to the same position relative to the Sun as seen from Earth.

• 月つきの会かい合ごう周しゅう期きは約やく29.5日にちです。

  The Moon's synodic period is about 29.5 days.