I have theoretical question. Let's assume that it is full moon and two different humans are looking at it at the same time. One human is for example in London and one in Beijing. It doesn't really matter where exactly, important is that they are almost on opposite side of Earth but they both see the moon at the same time. I assume they see the moon from different angle. Is it possible that one of them see different part of the moon because of this angle. It could be just the border, tiny part.

Could you please tell me, how big is this tiny part of the moon which one see and the other don't? Few meters? Kilometers?

Thanks everyone for help.


1 Answer 1


Yes, they do see a slightly different face of the Moon.

It's easy to calculate how different. If they're on nearly opposite sides of the Earth so that one sees the Moon just rising and the other sees the Moon just setting, they are seeing it from about 1.9 degrees apart. (A triangle with a base of 8000 miles (the distance they are apart) with sides of 240,000 miles (the distance to the Moon) yields an angle of 1.9 degrees (8/240 radians).

So they'll be viewing the Moon from 1.9 degrees apart and will see a full moon displaced by 1.9 degrees, or about 36 miles on the surface. So one will see 36 miles of Moon more on the Lunar east side than the other and the other will see about 32 miles more on the Lunar west side.

  • $\begingroup$ I'd add to that that the Moon spins as you change latitude. If you're familiar with the markings on the moon, sometimes seen as a face, and you travel to the other hemisphere, the moon's "face" will be upside down or, if you move about 90 degrees latitude, it might appear sideways. forbes.com/sites/jillianscudder/2017/09/09/… $\endgroup$
    – userLTK
    Jul 28, 2018 at 1:46
  • 2
    $\begingroup$ Well, be clear about this! It's you who spin and look at the moon while upside down! $\endgroup$
    – Mark Olson
    Jul 28, 2018 at 2:07
  • $\begingroup$ One will see 36 miles of the Moon more on the Lunar East side than the other and the other will see about 32 miles more on the Lunar West side? Shouldn't both the numbers be 36? $\endgroup$ Jun 24, 2023 at 16:16

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