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I've read in multiple sources that the Moon appears the other way up in Northern Hemisphere vs Southern Hemisphere. Here is one that explains why: Does the Moon look different in the northern and southern hemispheres?

My question is, where is the line drawn in this case where the moon 'flips'? Is it exactly the equator? I'm not sure if it is, the simple 'thought experiment' in the above link assumes (for simplicity's sake) that the orbit of the Moon is exactly above the equator. According to Wikipedia, the orbit of the Moon is slightly tilted, and our own earth also tilts from time to time. Where does the moon flip exactly? Does it change throughout the year as our earth change its tilt? If so, how? Which are the areas that always see the northern look or the southern one throughout the year?

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    $\begingroup$ This happens every time the moon passes overhead. In the eastern sky, the north pole of the moon is to the left and in the western sky, the north pole is to the right. $\endgroup$
    – LDC3
    Nov 10, 2018 at 15:17

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The moon doesn't flip. Is us who flip.

Those in the antipodes have their heads pointing in the opposite direction. So the moon appears inverted. But there is no sudden point where it "flips". We don't live on a discworld.

You can see this yourself. Because as the Earth spins you will change the direction in which your head is pointing. Look at the full moon over the course of one night. As it appears to travel from East to West in the sky, it's orientation will slowly change. There is no mystery here. You are being rotated by the Earth.

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  • $\begingroup$ of course, it is us who actually 'flips', sorry if the wording confuses you. As explained in the article I linked, according to where we are, when we look up to the moon, we do so in certain direction, which makes the moon look 'upside-down' compared to the other hemisphere. $\endgroup$
    – user69715
    Sep 20, 2015 at 16:26
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    $\begingroup$ As James Kilfiger pointed out, "The orientation is gradual." There is no place where it appears to flip. From our point of view, the moon appears to rotate about 1 degree for every 1 degree change in Latitude. Longitude doesn't matter, only Latitude. If you were on the space station, which takes only about 45 minutes to orbit 1/2 the circumference of the Earth and if the shuttle was on a perfectly north to south orbit, and you watched the moon , you'd observe the moon slowly spinning as well as moving across your field of view and it would do a full 180 degree "flip" over 45 minutes. $\endgroup$
    – userLTK
    Sep 20, 2015 at 17:48
  • $\begingroup$ That should be "station" was on a perfectly north-south orbit, not shuttle. $\endgroup$
    – userLTK
    Sep 21, 2015 at 0:33
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This doesn't really answer your question, but the orientation of the moon is changing constantly, because we tend to compare the moon to the horizon, and think of the horizon as fixed. Here's a video demonstrating the effect (simulated) for the full moon over London on August 28-29 (all times GMT):

https://www.youtube.com/watch?v=QXVpRfaJXmY

If you were changing location, you would see a similar gradual effect.

The only real place you would see a true "flip" is near where the moon is at zenith (overhead), because, as you passed the zenith point, the moon may go from being 89.999 degrees high in the western sky to 89.999 degrees high in the eastern sky (and flip directions because you're now comparing it to a different horizon).

Realistically, when the moon is that high, you probably wouldn't be comparing it to the nearest horizon.

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