3
$\begingroup$

The Moon is receding from the Earth, at a rate of about 4 cm per year. We can currently see about 59% of the Moon's surface, from the Earth's surface.

Will the amount of the Moon's surface we can see from Earth change (significantly) as the Moon recedes?

$\endgroup$
  • 3
    $\begingroup$ Oh this is a very cool question; in addition to having to check how eccentricity is predicted to evolve, if one wants one can include finite distance effects (we can't see a full hemisphere if too close) and even consider views from opposite sides of the Earth (i.e. full moon near sunset at one place and near sunrise at another) $\endgroup$ – uhoh Aug 10 at 15:33
  • 1
    $\begingroup$ "Significantly?" How much of a change would you consider to be significant? Also, over what time span? It's going to be a while before the Earth's own rotation becomes tidally locked to the Moon's orbit. $\endgroup$ – Solomon Slow Aug 10 at 21:09
  • $\begingroup$ @SolomonSlow I don't understand what Earth's rotation becoming locked has to do with this question $\endgroup$ – uhoh Aug 11 at 0:42
  • 1
    $\begingroup$ I'd guess, as the Moon moves away from the Earth it's orbit will become more eccentric and we'll see more than 59%. This change is obviously going to be incredibly gradual. In a billion years, the Moon will be maybe 10% further (based on 3.8 cm per year) and probably less than that due to the effect diminishing with distance. I suspect, the Laplace plane with continue to dominate the Moon's orbit, so greater solar perturbation and higher eccentricity. The math behind this stuff is hard. Loosely related: astronomy.stackexchange.com/questions/36512/… $\endgroup$ – userLTK Aug 11 at 3:19
  • $\begingroup$ @uhoh, What do you suppose supplies the energy that lifts the Moon out of Earth's gravity well (i.e., causes it to "recede from the Earth?") The answer is, tides. The tides on Earth gradually slow the Earth's rotation, and transfer kinetic energy to the Moon's orbit. en.wikipedia.org/wiki/Moon#Tidal_effects The Moon eventually would stop receding, and the Earth eventually would always present the same face to the Moon if not for the Sun, which is on-track to swallow up both the Earth and the Moon in about five billion years from now. $\endgroup$ – Solomon Slow Aug 11 at 12:12

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Browse other questions tagged or ask your own question.