Synodic
A synodic cycle begins with a conjunction of two heavenly bodies and ends with their next conjunction, after one of them has completed an orbit and then caught up with the slower body. If the name of the cycle contains two planets, for example, the Jupiter-Saturn synodic cycle, it refers to the conjunctions of those two planets.
If the name only contains one planet, for example, the Jupiter synodic cycle, it refers to Jupiter conjunct the earth from a heliocentric perspective. From a geocentric perspective that would be the sun-Jupiter opposition, i.e. when Jupiter is retrograde. In the case of the inner planets, the cycle begins with the inferior conjunction, when the planet is retrograde and between the earth and the sun.
A synodic day is the period it takes for a planet to rotate once in relation to the body it is orbiting. For Earth, the synodic day is known as a solar day, and is about 24 hours long.
The synodic day is distinguished from the sidereal day, which is one complete rotation in relation to distant stars. A synodic day may be "sunrise to sunrise'" whereas a sidereal day can be from the rise of any star to the rise of the same star on the next day. These two quantities are not equal because of the body's movement around its parent.
The period between two new moons is called a Synodic Month.
It is 29.53 days long on average.
See also
Weblinks
- The Sidereal and Synodic Months - Animation (Freedman and Kaufmann, 2004)
- Sidereal and Synodic Periods of the Moon (Illustration)