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Astronomy

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    $\begingroup$ "...Mercury is not only the closest planet to Earth..." Hmm... Mercury is not the closest planet to Earth. Venus is the planet that gets closest to Earth. $\endgroup$
    – uhoh
    Commented Nov 1, 2021 at 0:44
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    $\begingroup$ To follow up on uhoh's comment, Mercury is not the closest planet to any planet expect Venus. There is an oddity where Mercury is -On Average- the closest planet to Earth because Venus' orbit carries it to the far side of the Sun further than does Mercury's. Is that what you're asking about? $\endgroup$
    – JohnHunt
    Commented Nov 1, 2021 at 1:23
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    $\begingroup$ @JohnHunt Yes, I'm talking about average. Mercury is indeed the closest planet (on average) to Earth, and to all other 7 planets as well. $\endgroup$
    – Gerardo Furtado
    Commented Nov 1, 2021 at 2:54
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    $\begingroup$ Warning make sure you identify what the parameter is that you are averaging over! I suspect most of us expect the average with respect to time. But if one chooses to take the average over, say, angle of the orbits ( rho -theta coordinates), things will come out rather differently. $\endgroup$
    – Carl Witthoft
    Commented Nov 1, 2021 at 13:25
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    $\begingroup$ @Constantthin it's talking about the average over the path. The places when planet B is in-line sun-side and opposite side cancel each other out to average the same as the planet A's orbital radius irrespective of the radius of B. In the places when planet A, the sun and planet B form a triangle, the AB distance is the longest side of a triangle where the other two sides are the orbital radii of A and B, so the bigger the orbital radius of B the bigger that triangle is, and so the bigger the average distance between A and B. $\endgroup$
    – Pete Kirkham
    Commented Nov 1, 2021 at 18:14