Chapter 3: Problem 9

What is the difference between a sidereal month and a synodic month? Which is longer? Why?

Short Answer

Expert verified

The difference between a sidereal month and a synodic month lies in what they are based on. A sidereal month, about 27.3 days, is measured by the Moon's orbit relative to the stars, while a synodic month, about 29.5 days, is measured based on the phases of the Moon. The synodic month is longer because the Earth also moves around the Sun in the time it takes for the Moon to complete one orbit of the Earth.

Step by step solution

Definition of Sidereal Month

Sidereal month refers to the lunar cycle that is measured by the Moon's orbit relative to the stars. It is the time it takes for the Moon to return to the same position in the sky as referenced to the stars. This period lasts approximately 27.3 days.

Definition of Synodic Month

Synodic month refers to the lunar cycle that is measured based on the phases of the Moon. It is the period from one New Moon to the next New Moon. This period lasts approximately 29.5 days.

Comparison and Explanation

The synodic month is longer than the sidereal month. This is because the Earth is also moving around the Sun. In the time it takes for the Moon to complete one orbit of the Earth (sidereal month), the Earth has moved in its orbit around the Sun. Thus, it takes a little longer for the Moon to return to the same phase (synodic month).

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What is the difference between a sidereal month and a synodic month? Which is longer? Why?

Short Answer

Step by step solution

Definition of Sidereal Month

Definition of Synodic Month

Comparison and Explanation

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