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"Appear" to wobble is an important part of the idea. This is an apparent motion of the moon and not a true motion. It is called east-west libration (from Libra, the scale). It happens because of the combination of these essential facts:

  1. The moon's orbit around the earth is an ellipse and not a circle.
  2. Objects in elliptical orbits move in their orbital paths more quickly when they are closer to the objects they are orbiting, and less quickly when they are farther away. The moon's maximum orbital velocity happens when the moon is at perigee (closest to earth).
  3. The rate of the moon's rotation (turning on its axis) is for our purposes a constant velocity.
  4. The moon is tidally locked with earth, meaning that it rotates exactly once during every sidereal [absolute] orbit around earth. This is why the same face of the moon, for the most part, is always oriented toward earth.

Now if you view the moon from the earth in a time lapsed version of the moon's orbit, something interesting happens. When the moon is getting nearer and nearer to perigee, it picks up speed in its orbit. But its rotational speed is almost exactly constant. So the moon moves in its orbit 'ahead' of its rotation, in a sense. We get a glimpse of the leading edge, or limb, of the moon. Then, when it is past perigee and starting to slow down in its orbit, its rotational speed moves ahead of its orbital speed, and we get a glimpse of the trailing edge or limb of the moon. Observing this with software, you can see the obvious apparent wobble of the moon. There is also north-south libration which happens for different reasons.

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โˆ™ 2011-03-09 23:47:24
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The Moon

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Approximately how long is the period of time from the new moon to the full moon phase

More than half of the moon is illuminated

Right half of moon is illuminated

At what point does the southern hemisphere have the greatest exposure to the sun

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Q: Why does the moon appear to wobble as it completes its cycle?
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Related questions

How long does it takes the moon to complete a waxing and waning motion?

The moon completes an entire cycle of all of its phases in 29.53 days.


How long does it takes the moon to complete a waxing waning motion?

The moon completes an entire cycle of all of its phases in 29.53 days.


Does the moon orbit the earth once a day?

It takes the moon roughly 28 days to orbit the earth. The moon completes the cycle approximately 13 times a year.


The Moon completes one orbit around the Earth in approximately and completes one cycle of its phases in approximately?

It is 27 1/3 days, 29 1/2 days.


Which phase of the moon completes the moon?

Full moon.


How is it the moon calendar taken?

A moon calendar is created by carefully observing the phases of the moon and recording them. The moon completes a cycle approximately once every 28 days, which is the time elapsed between two full moons.


Why does the moon seem to pass close to other planets during its orbit?

The satellite that orbits the planet Earth is called Moon, and completes a complete orbit cycle once every 27.32 days. The Moon may appear closer to other planets at times because the path the Moon takes around the Earth is elliptical, meaning more oval then circular.


Why was the calendar first based on the moon?

Because of the regularity of the lunar phases. The Moon completes a cycle, from Full Moon to New Moon back to Full Moon in about 28 days. It was probably chosen as a marker for the passage of time based on observation of this regularity.


How long does it take the moon to orbit the Earth in one complete cycle?

Viewed against the background of distant "fixed" stars, the moon completes one orbital revolution in 27.32 days. Observing the "phases" of the moon from Earth, it displays a complete cycle of shapes every 29.53 days.


How long does it takes the moon to orbit the earth in one complete cycle?

Viewed against the background of distant "fixed" stars, the moon completes one orbital revolution in 27.32 days. Observing the "phases" of the moon from Earth, it displays a complete cycle of shapes every 29.53 days.


Does a full moon appear in the middle if the moon cycle?

Yes, a full moon appears after waxing and before wanning. A new moon comes before waxing and after wanning


How long is the lunar cycle?

The Moon completes an orbital revolution around the earth in 27.32 days, and it displays a complete cycle of 'phases' in about 29.53 days, which is approximately a month. (More precisely 29.53059 days.)

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