Sidereal vs. Synodic

Difference Between Sidereal and Synodic

Sidereal and Synodic, both are two astronomical terms. Both these terms are associated with the period of celestial bodies in orbit. Here are some of the differences between them:

  • Sidereal is the time taken by the stars in completing one period while Synodic is the time taken by a solar body for completing one period.
  • The location of objects in respect to sun is known as the Synodic period while the location of objects in respect to stars is known as Sidereal period.
  • A sidereal day is equal to the rotation of the Earth once in a day in respect with the stars while a synodic day is the rotation of Earth once in a day in respect to the Sun.
  • The period between one full moon and another full moon is known as Synodic cycle. It is an interesting fact that sidereal month and synodic month are of different periods. The synodic month is longer than sidereal month.
  • A sidereal month is of 27 days, 7 hours and 43 minutes while synodic month has 29 days, 12 hours and 44 minutes.

‘Sidus’ is  Latin word which means star and it is known to be the base for the word sidereal while ‘synodic’ is believed to be derived from Greek word ‘synodos,’ which means ‘meeting of two things’.


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