Assuming a situation similar to this, where the moon causes slower but massive tides that slowly encircle the globe. Would the poles be constantly underwater or not underwater (like A or B below)?:

enter image description here

Or would it depend on the moon?

Main question: Would a massive tide be closer to A or B or C(something else)?

  • $\begingroup$ Related: worldbuilding.stackexchange.com/questions/19503/… $\endgroup$
    – dot_Sp0T
    Sep 27, 2018 at 13:07
  • $\begingroup$ Somehow your images make me crave a martini. $\endgroup$
    – Willk
    Sep 27, 2018 at 13:19
  • $\begingroup$ On a serious note, carve off the shipbuilding question to its own, please. I got nothing for the tides, only the ship and I feel bad to just answer one of the 2 questions (both good!) that you pose here. $\endgroup$
    – Willk
    Sep 27, 2018 at 13:24
  • $\begingroup$ @Willk see worldbuilding.stackexchange.com/questions/126107/… $\endgroup$
    – depperm
    Sep 27, 2018 at 13:37
  • $\begingroup$ The question seems to stem from very common misconception, that the tides are caused by the Moon just pulling the water towards itself. No, the tides are caused by the Moon actually deforming the Earth, squishing it slightly, because of the different directions and magnitudes of the gravitational force around the globe. $\endgroup$
    – vsz
    Sep 27, 2018 at 20:26

1 Answer 1


You cannot have neither A or B. Of the two, B is the more implausible: the water is being pulled in 3 directions (up, right and down) by a single moon.

About A, I would expect the two spheres (solid and liquid) to share the same rotation axis, and thus a non zero tidal height also on the side opposite to the moon, more or less like it happens on Earth.

tide height

The poles would practically experience constant low tides.

A situation like A or B would not be happening around one of the principal axis of inertia, and therefore could not happen spontaneously.

  • $\begingroup$ To clarify: the tides are highest directly in line with a moon, lowest at 90 degrees off (along the ecliptic), and intermediate at the poles. $\endgroup$
    – Skyler
    Sep 27, 2018 at 18:25
  • 1
    $\begingroup$ I don't think explaining the antipodal maximum involves any rotation at all. You just have to realise that Earth is in free fall towards the moon, which means in its reference frame the Moon's gravity is zero at the centre of Earth, and therefore negative at the further surface. $\endgroup$
    – Jan Hudec
    Sep 27, 2018 at 18:44

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