EDIT:Recently , I have been observing the moon and i realised the moon seems to be moving very quickly from one place to another, and back to its initial position in a short cycle(few minutes),the movement seems like it's moving back and forth about some axis at very small radius., I don't think this is due to orbital motion around Earth , conz the movement should be very insignificant given that a complete cycle is a calendar month.

Here is my theory: On the day I observed the moon was quite cloudy , I thought there were many clouds in front of the moon which caused uneven refraction due to uneven cloud layers with uneven thickness passing by, hence the moving line of sight slightly deviates .

However, I realise even I observe the moon directly in clear sky, it seems to move pretty quickly and back to its original position in a short time, why is it like that? Is it due a phenomena so called libration?

PS i'm observing the moon just by naked eye.

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    $\begingroup$ How long is the cycle? Minutes? Hours? And what path does the Moon trace as it moves round the cycle? $\endgroup$ Sep 8, 2014 at 17:00
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    $\begingroup$ It has probably to do with your eye moving and with the brain being unable to adjust to it due to a lack of reference points. I have observed the same effect looking at a digital clock in a dark shakey bus. $\endgroup$ Sep 8, 2014 at 17:45
  • $\begingroup$ Do you see the same effect when you look at a bright star? $\endgroup$
    – garyp
    Sep 8, 2014 at 17:50
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    $\begingroup$ How big is the movement relative to the size of the moon, since it might be possible that the sky is turbulent and causes the moon to reform/move a bit in the sky. $\endgroup$
    – fibonatic
    Sep 8, 2014 at 17:57
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    $\begingroup$ @fibonatic it'd have to be a rather large isoplanatic patch (with a large difference from its neighbor atmosphere) to move the entire image of the moon! $\endgroup$ Sep 8, 2014 at 19:40

1 Answer 1


The only way to measure "motion" of the moon is relative to objects in its (close) vicinity. In your case, the only objects might be stars, or clouds. Clouds are a terrible reference object; and if there were any optical effects in the sky, the stars would move in concert with the moon.

Our ability to look at an object in the distance without any reference, and determine that it is moving, is not very good. Please repeat your measurement with a solid camera on a tripod, pointing at a fixed point in the sky. And recognize that there are people who observe the moon for a living, with very powerful telescopes. I think they would have noticed...

Libration is the phenomenon that makes it possible to see a little more than 50% of the moon's surface (though not all at the same time) - but as you surmise, that doesn't cause the apparent center of the observable moon to jiggle in orbit.

I agree with the comments - you will find that the issue goes away when you improve your measurement setup. The naked eye was not made for this kind of thing.


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