Home >> Science & Nature >> Astronomy

How to Calculate Synodic

The synodic period is an astronomical term used to describe the orbit of a planet or a moon. It expresses the amount of time it takes for an object to return to a specific position. This expression is complicated by the fact that the position being considered is not a universal position but merely a relative one. To return to the same synodic spot in the cosmos is, in fact, only to be in the same position relative to two other moving objects in outer space (usually the Earth and the sun). A good example of synodic periods applied to real life can be found in the lunar phases. Due to the relative motions of the Earth, the moon and the sun, each new moon can be said to represent the completion of a cycle through the moon's synodic period.

Things You'll Need

Formula: S = 1 / abs(1/E-1/P)

Instructions

- 1
  Determine the sidereal periods of the two objects involved. The sidereal period is the amount of time it takes for the object to make one trip around the sun. For a list of sidereal periods for different objects, see the link in Resources.
- 2
  Insert the data gathered from Step 1 into the formula: S = 1 / abs(1/E-1/P)., where S = synodic period, E = sidereal period of the Earth, P = sidereal period of the second object and abs = the absolute value operation.
  For example, to determine the synodic period of the Earth's moon, we would use this same formula. The sidereal period of Earth is "1" and the sidereal period of the moon is "0.0748." After we inserted this information into the formula, we would get: S=1 / abs(1/1 - 1/0.0748).
- 3
  Solve for S. Using our example, this would give us:
  S=1 / abs(1/1 - 1/0.0748).
  S= 1 / abs(1 - 12.8)
  S= 1 / abs(-11.8)
  S=1/11.8
  S=0.08
  Therefore, 0.08 would be the synodic period for the moon.

Astronomy