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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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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.


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.


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 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.


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


Is the earth a stationary object in the lunar sky?

No, it is not. This will seem wrong to people who are aware that the moon's orbit it tidally locked with earth. Observed over a long enough period, the moon has a distinct wobble that comes from what is called libration. It results from the fact that the moon's orbital velocity around the earth is not constant, while the moon's rotational velocity is for all practical purposes constant. So the earth will appear to move a bit in the lunar sky. This is an apparent motion and not a true motion. It occurs to me that there must be places on the moon where the earth would appear, over the course of a lunar cycle, unable to decide whether to rise or to set! It would appear to bob up and down at the moon's horizon.


Why does the earth not wobble very much?

i believe it is based of the pull of the earth to the moon on gravity which is why the earth does not wobble as much if you know what i mean.


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.)


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.


Is the moon rotating faster than earth?

No. The moon rotates much slower than Earth. Earth completes a rotation once every days. The moon completes a rotation once every 27 days.


How do we use the moon's phases to tell time?

The phase of the moon can in principle tell you where the Sun is, and that in turn can tell you what time it is. However, most people don't do that, and instead just use the moon's phases to count the days. The moon completes a full cycle of phases in just about a month.


Why does the moon appear to pass through phases as it completes one revolution around the Earth?

One side is always dark; the amount of the dark part we see is dependent upon the angle at which we see it. This angle changes as the moon revolves.


How long deos it take for the moon to orbit the earth?

The moon completes one orbital revolution around the earth in 27.32 days. The moon also completes one rotation on its axis in exactly the same time.


How many days does moon take to rotate?

The moon completes one rotation on its axis, and also completes one orbital revolution around the earth, in 27.32 days. (rounded)


What is different about the crescent phase that precedes length of the new moon and that which follows the new moon phase?

The first crescent after New Moon and last crescent after New Moon appear on opposite "sides" or edges of the moon's disk. Viewed from here in the USA, the crescent at the beginning of the cycle of phases, after New Moon, is on the right-hand side of the moon. The crescent at the end of the cycle, before New Moon, is on the left-hand side.


How did the moon appear between the fullmoon and the halfmoon?

It will appear as a Gibbous moon (3/4 of a full moon).


How long does the moon rotate?

The moon is always rotating. It completes a full rotation every 27.32 days.


How many months does the moon take to complete its orbit?

The moon completes an orbit relative to the Earth in 27.32 days. It also completes an orbit relative to the sun in 365.24 days on the average.


Why is the cycle of the moon important?

The cycle of the moon is important because it effects the tide.


Does the shape of the moon appear the same?

The moon does have a slight wobble, and sometimes it's closer to Earth, while other times it's farther away. But the shape of the moon changes all the time - it's called "phases". Every month the moon goes from new (no moon at all), to crescent, to half full, to full - then it shrinks back to half moon, crescent, until it disappears into the sun's glare and becomes the new moon again.


What phase is it when the moon is halfway through the lunar cycle?

The moon will be a full moon, halfway through the lunar cycle.