Difference Between Sidereal and Synodic

Sidereal vs Synodic
 

Sidereal and Synodic are to be understood as two different terms used in astronomy with significant difference between them. In fact, both of them are related to the period of bodies in orbit. Sidereal is nothing but the time required for the stars to complete a period. On the other hand, Synodic is the time required for the solar body to complete a period. This is the major difference between Sidereal and Synodic. To explain it better, a Sidereal Day is the time it takes for a star to come back to the exact position it was before. A Synodic Day is the time it takes for the Sun to pass the observer’s meridian successfully. Both the terms are derived differently from their root words. ‘Sidus’ is a Latin word for star and it is said to be the basis for the formation of the word sidereal. On the other hand, the word synodic is said to have been derived from the Greek word ‘synodos,’ which means ‘meeting of two things’.

What is Sidereal?

Sidereal is an important term in astronomy. The position of objects with respect to the stars is called the Sidereal period. A sidereal day amounts to the rotation of the Earth once a day in relation to the stars. For a Sidereal day to pass, the Earth has to rotate 360 degrees. That is when the star comes back to the exact position it was before. It is interesting to note that the Sidereal month is short. A sidereal month is said to be of a duration of 27 days, 7 hours and 43 minutes.

What is Synodic?

The position of objects with respect to the Sun is called the Synodic period. When it comes to a Synodic day, a Synodic day refers to the rotation of the Earth once a day in relation to the Sun. You may think that it means the Earth has to rotate only 360 degrees. However, that is not the case. As Earth is also continuously moving around the Sun, the Earth has to rotate a little more than 360 degrees to have the Sun at the observer’s meridian. Synodic Day is also known as Solar Day. It is interesting to note that Synodic month is longer. In other words, the Synodic month is said to be somewhat longer than the sidereal month.On the other hand, a Synodic month is said to last for a period of 29 days, 12 hours and 44 minutes. The time period from one full moon to another full moon is called Synodic cycle.

What is the difference between Sidereal and Synodic?

• Sidereal is nothing but the time required for the stars to complete a period. On the other hand, Synodic is the time required for the solar body to complete a period. This is the major difference between Sidereal and Synodic.

• A Sidereal Day is the time it takes for a star to come back to the exact position it was before. A Synodic Day is the time it takes for the Sun to pass the observer’s meridian successfully. Synodic Day is also known as Solar Day.

• The position of objects with respect to the Sun is called the Synodic period. On the other hand, the position of objects with respect to the stars is called the Sidereal period. This is another important difference between the two terms.

• It is interesting to note that the two types of months, namely Sidereal month and the Synodic month differ in terms of their duration. The Synodic month is said to be somewhat longer than the Sidereal month.

• To be exact, a Sidereal month is said to be of duration of 27 days, 7 hours and 43 minutes. On the other hand, a Synodic month is said to last for a period of 29 days, 12 hours and 44 minutes.

• To complete one Sidereal day, the Earth has to rotate 360 degrees. However, to complete one Synodic day, the Earth has to rotate little more than 360 degrees.

These are the differences between Sidereal and Synodic. As you can see, Sidereal is related to the stars while Synodic is related to the Sun.

Images Courtesy:

1. Sidereal and Synodic Day by Gdr (CC BY-SA 3.0)