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NurseJ23 NurseJ23
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11 years ago
what i have to the rotation is 27 1/3 days and the revolution is 29.5 days. am i correct?
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wrote...
11 years ago
yes
wrote...
11 years ago
Not quite correct.  The time for the Moon to make one complete orbit of the Earth and one turn on its axis is 27 1/3 days.  This is called the sidereal period, or star-to-star.  It is measured against the background star fields.

The 29.5 day phase-to-phase, or synodic period, is the time the Moon takes to return to the same phase.  This is a measurement with respect to the Sun.  Because the Earth is moving in its orbit with respect to the Sun, the Moon must travel slightly more than one orbit to return to the same position relative to the Sun and the Earth.  That extra travel time results in the 29.5 synodic period.

The Moon's rotation rate is the same as its orbital period.  As it orbits the Earth it turns on its axis at a rate that keeps the same face towards the Earth during the whole orbit.  This rotation period is almost exactly the same as its sidereal period or 27 1/3 days.
wrote...
11 years ago
No, you are not correct.

Since the Moon is tidally locked with the Earth (the same side of the Moon always faces the Earth) the Period of Rotation and Period of Revolution of the Moon are exactly the same (27.322 days).  This is called the "Sidereal Month".  If they were different you would see that the Moon was slowly turning, and you would eventually see the other side of the Moon facing the Earth.

A complete cycle of the phases of the Moon takes 29.531 days, because of the revolution of the Earth around the Sun.  This is called the "Synodic Month".

Watch the animation in the following link to understand.
http://www.sumanasinc.com/webcontent/animations/content/sidereal.html
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