I find it funny that the moon is the only object in the solar system to almost perfectly fit the sun, resulting in the spectacular solar eclipses. No other object except maybe a few irregular moons like Pandora from Saturn would do that, and for them, they aren't round, and thus can't fully block out all light. The moon also has a perfect rotation that is almost exactly the same as Earth's rotational period, resulting in a tidal lock, which causes tides.

Is this a coincidence? Any speculation on why this happens? Is this the only observed place where such criteria play into such perfect coincidence?

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    $\begingroup$ If it were really special, there would be a total eclipse every new Moon and every Full Moon. :-) $\endgroup$
    – JohnHoltz
    Commented Mar 15, 2019 at 2:43
  • $\begingroup$ @JohnHoltz well its orbit is tilted, but still these two coincidences... what resulted in them? $\endgroup$
    – Max0815
    Commented Mar 15, 2019 at 2:47
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    $\begingroup$ -1 and vote to close for primarily opinion-based for explicitly requesting speculation! $\endgroup$
    – uhoh
    Commented Mar 15, 2019 at 5:15
  • $\begingroup$ The moon also has a perfect rotation that is almost exactly the same as Earth's rotational period What?! The Moon's rotational period is nearly 30 times longer than Earth's. $\endgroup$
    – PM 2Ring
    Commented Mar 15, 2019 at 6:17
  • $\begingroup$ First about Moon's roundness: Moon is pretty big, so its gravitation forces pull down all of the material so it shapes round. And about "coincidence": there are a lot of moons in the Universe. Some of them are rounded and have the same angular diameter as their star. But this isn't so rare. $\endgroup$
    – User123
    Commented Mar 15, 2019 at 17:28

1 Answer 1


If the "perfect rotation" you describe is the fact that same face of the moon always faces the earth, this is explained by the 'Giant Impact Hypothesis' which also explains the formation of the moon. The molten earth was impacted by a large mass causing a part of the liquid earth to be flung out into space creating the moon. For a time, the two celestial bodies to be (the earth and moon) were connected to one another by some bridge of mass until eventually the centripetal force of their rotation finally pulled them apart. In fact, the two bodies are still moving apart today.


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    $\begingroup$ It should be noted that the radius of the Moon's orbit is increasing today for different reasons. In fact, a question on that very topic was asked by OP very recently on this Stack - but it's a duplicate. $\endgroup$ Commented Mar 15, 2019 at 7:42

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