4 ms·
Dang.. it never occurred to me how big the moon is. Looking at this picture, it's hard for me to comprehend why the moon would orbit the earth and not fall int
by vinhboy 11y ago
Dang.. it never occurred to me how big the moon is.
Looking at this picture, it's hard for me to comprehend why the moon would orbit the earth and not fall into the sun.
- Retric 11y agoIf you take the earth away the moon would still be orbiting the sun. So sure, the moon is far from the earth, but that just means it takes ~28 days to orbit the earth. PS: The moons orbit is actually 29.5 or 27.3 days depending on how you count it.
- Tuna-Fish 11y agoThe 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.
- scott_s 11y agoTunaFish and Retric gave great explanations, but I want to add a quick conceptual point: the moon (and the Earth) is falling into the sun. Constantly. It's just that the moon (and the Earth, and the other planets) have so much velocity tangential to the direction of the sun that instead of falling into the sun, they fall around the sun. That's what an orbit is.
- murbard2 11y agoThe moon is falling into the sun, just like the earth.
- dredmorbius 11y agoFalling but missing the ground. RIP D.A.