The gravitational pull the Sun has on the Moon is roughly two times greater than the pull the Earth has on the Moon. If this is the case, why does the Sun's gravity not pull the Moon away from the Earth?

  • $\begingroup$ Because both the Moon and the Earth are falling freely around the sun. The only effective forces the Moon feels from the sun are the tidal forces it creates at the orbit of Earth. $\endgroup$ – CuriousOne May 17 '16 at 21:35
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    $\begingroup$ Possible duplicates: physics.stackexchange.com/q/92465/2451 and links therein. $\endgroup$ – Qmechanic May 17 '16 at 21:36
  • $\begingroup$ If you like this question you may also enjoy reading this Phys.SE post. $\endgroup$ – Qmechanic May 17 '16 at 21:38

The Sun pulls on the Earth as well. So both Earth and Moon are "falling towards the Sun" all the time, just as they are moving in almost the same orbit.

Earth causes the orbit of the Moon to "wobble" a little bit. If you were simply given the coordinates of the Moon as it moves around the Sun, you would notice there is a deviation from the expected ellipse - which tells you there is "something else" there. But the Moon never goes into retrograde motion - in other words, it "keeps going forward" in its orbit, with just a little wobble.

The fact that we think the Earth is "holding on" to the Moon comes from our geocentric view of the universe.

  • $\begingroup$ I am not comprehending your explanation. How about when the moon is in between the earth and sun. At that point the sun should pull the moon out of Earth's orbit? $\endgroup$ – damx May 17 '16 at 22:59
  • $\begingroup$ The sun pulls on the earth as well as on the moon - both move (accelerate) towards the sun together! Think about Galileo's experiment on the tower of Pisa. $\endgroup$ – Floris May 17 '16 at 23:57
  • $\begingroup$ I get it now. You are probably referring something such as what is written in this paper. malagabay.wordpress.com/2012/11/03/… $\endgroup$ – damx May 18 '16 at 3:17
  • $\begingroup$ Actually that is a lot deeper that what I was talking about. Two objects circling the sun will both accelerate towards it at the same rate - so while the sun pulls harder on the moon than the earth does, the sun also pulls on the earth - so moon and earth, both experiencing a pull from the sun, accelerate towards the sun together. Moon and earth are close enough together that there is not much difference in the strength of the sun's gravitational field as they orbit each other. $\endgroup$ – Floris May 18 '16 at 3:21
  • $\begingroup$ deeper and logical. $\endgroup$ – damx May 18 '16 at 3:57

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