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Doesn't every planet? I'd be astonished if every planet completed a revolution in a perfect multiple of rotation time. Wouldn't it would have to be an engineere

• twic 7y ago
  > But there is one planet where the calendar would need zero finessing: Mercury. The small planet revolves exactly three times, or days, over the course of two years — allowing its calendar to naturally align every other year. I would imagine that this is some form of resonance, like the tidal locking of the moon, but i can't explain it myself.
  • Sharlin 7y ago
    It is indeed: > In some cases where the orbit is eccentric and the tidal effect is relatively weak, the smaller body may end up in a so-called spin–orbit resonance, rather than being tidally locked. Here, the ratio of the rotation period of a body to its own orbital period is some simple fraction different from 1:1. A well known case is the rotation of Mercury, which is locked to its own orbit around the Sun in a 3:2 resonance. https://en.wikipedia.org/wiki/Tidal_locking https://en.wikipedia.org/wiki/Tidal_locking
  • gowld 7y ago
    It rotates three times per 2 revolutions, right?