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The gravitational influence of the Sun on the Moon is greater than the gravitational influence of the Earth. In a very real way, the moon is orbiting the Sun.
by Tuna-Fish 11y ago
The gravitational influence of the Sun on the Moon is greater than the gravitational influence of the Earth. In a very real way, the moon is orbiting the Sun.
However, the orbit it flies around the Earth only very slightly modifies it's orbit around the Sun. The lunar orbital speed around the earth is ~1km/s, while the orbital speed around the sun is ~30km/s. That is, it never loops backwards on it's path around the sun, it's orbital velocity is at most only reduced by about 3%.
Picture from wikipedia: https://en.wikipedia.org/wiki/File:Moon_trajectory1.svg https://en.wikipedia.org/wiki/File:Moon_trajectory1.svg
- rootbear 11y agoNice illustration in wikipedia. I first learned about this feature of the moon's orbit from one of Isaac Asimov's science essays. In many ways, the Earth and Moon are like a double planet, though not so much as Pluto and Charon.
- sahaj 11y agoIs this also true of Jupiter's moons?
- Tuna-Fish 11y agoNo. Europa and all the moons closer to Jupiter than it do in fact occasionally travel backwards in relation to their orbit around the Sun. This is also true of Dione and all the moons of Saturn lower than it, all the inner moons of Uranus, and all the regular moons of Neptune. The gas giants are much more massive than earth, while also being much further away, and many of their moons orbit closer to them. This all combined makes some of their moons pulled more strongly by them than they are pulled by the sun.
- vinhboy 11y agoDude this is amazing. I did not know this. TIL.