Hmm... ages since I studied physics. If the orbit is stable & circular, the gravitational force and centripetal force should be equal. The mass of the moons cancels out, and so the higher radius orbit is normally slower. So... the higher orbit moon is elliptical or decaying?
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Replying to @TomMostlyZen @OortCloudAtlas
Here is another one: if Jupiter rotates around itself in 9h, and the moon around Jupiter in 42h, why does the moon appear to be moving at a higher velocity than the surface below it, despite being seen from 10 Mio km?
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Replying to @Plinz @OortCloudAtlas
Ok, is Jupiter actually rotating towards the left of the camera and the apparent motion of the moons actually the fact that they are falling behind, relative to the rotation of the eye of the storm? But then that would mess with my answer to the first riddle...
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Replying to @TomMostlyZen @OortCloudAtlas
I know, right? If you are a proper physicist you won't sleep tonight
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Jupiter is really rotating to the right (anti clockwise when seen from the north pole), of course, and so are the moons, and afaik Cassini was passing it from left to right at a distance of 140 radii, while Io was at 24 radii...
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Replying to @Plinz @OortCloudAtlas
Was the camera upside down? So north pole is at bottom? Then my earlier answer would make sense because it looks like the storm clouds are moving to the left, and that’s the only way that the planets could be falling behind and the outermost planet falling behind more quickly
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Replying to @TomMostlyZen @OortCloudAtlas
The Red Spot is below the equator, so probably no
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Replying to @Plinz @OortCloudAtlas
Ok. It’s a time lapse movie, assembled from many photographs. Someone at NASA fucked up and compiled the series of photographs BACKWARDS. North Pole is at top, but rotation appears to be toward left, with planets falling behind Jupiter’s rotation and appearing to move right
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Moons must be falling behind rotation of planet because outermost moon (Europa) appears to be moving faster but Europa orbits slower than Io as it’s at the higher orbit. So planet must be rotating left as it appears to be.
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Anyway, Cassini went to Saturn. It only flew by Jupiter. So either it is Cassini doing a flyby rather than being in orbit, in which case it could have been flying contra to the orbital rotation, or it was actually filmed by Juno in orbit and filmed backwards or upside down.
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You can look up the trajectory. It was a flyby. Yes, I think the video is played backwards.
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Replying to @TomMostlyZen @OortCloudAtlas
But the outer moon is still faster
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