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The sun does move on Mercury. Mercury is not tidally locked- it has a 3:2 spin-orbit resonance. I.e., it rotates 3 times for every two times it goes around the
by gliese1337 11y ago
The sun does move on Mercury. Mercury is not tidally locked- it has a 3:2 spin-orbit resonance. I.e., it rotates 3 times for every two times it goes around the sun. This means that the two sides of the planet alternate facing the sun at perihelion.
- mikeash 11y agoInteresting tidbit about Mercury's rotation: although it's clearly visible to the naked eye and thus has been known since before the dawn of recorded history, and has been observed through telescopes since telescopes were invented, the fact that it is not tidally locked has only been known since 1965.
- lmm 11y agoMercury is pretty featureless, right? It's not like Jupiter where you could see the rotation just by keeping track of the Great Red Spot.
- mikeash 11y agoIt has lots of craters and such. I don't know what it looks like through an older telescope. According to Wikipedia, the problem was that because the rotation is in a resonance with its orbit, and because it's so close to the sun and thus can only be observed at certain times, it was always observed when in just one orientation.