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LoveKnowledge
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Just wanted to make sure..
brainstorm said:Why wouldn't/isn't the sun's gravitational pull on the moon noticeable in its orbital shape? I would think it should be much farther from the Earth when closer to the sun and much closer to the Earth when on the side away from the sun. Does Earth's pull on the moon somehow neutralize the sun's effects on it?
The Earth's pull does not in any way neutralize the sun's effect on the moon. In fact, the sun's pull on the moon is about double the Earth's pull on the moon. The sun's pull on the moon can vary between 4.2E20 N and 4.5E20 N if everything lines up just right. The Earth's pull on the moon can vary between 1.8E20 N and 2.2E20 N. So even the Earth's strongest pull is about half of the sun's weakest pull on the moon.brainstorm said:Why wouldn't/isn't the sun's gravitational pull on the moon noticeable in its orbital shape? I would think it should be much farther from the Earth when closer to the sun and much closer to the Earth when on the side away from the sun. Does Earth's pull on the moon somehow neutralize the sun's effects on it?
The semimajor axis of the Earth is about 3 orders of magnitude larger than the semimajor axis of the moon. The mass of the sun is about 6 orders of magnitude larger than the mass of the earth. Since the radius is squared in Newton's law of gravitation the effects of the sun's larger mass and the Earth's closer distance are both about 6 orders of magnitude. The sun actually wins the gravitational tug of war, but by less than an order of magnitude.Pengwuino said:The distance from the Earth to the Moon is orders of magnitude less than the distance from the Moon to the Sun. Though, the mass of the Earth is orders of magnitude less than the Sun, but you can do the calculation and the Earth should certainly dominate as far as who wins the gravitational tug of war.
By that I assume you mean that the since the gravitational force exerted by the Sun on the Moon is about twice that exerted by the Earth then the Moon should escape the gravitational influence of the Earth.cosmos 2.0 said:by this calcn the moon should go around the sun rather the Earth - is there something i am missing here ?
The Sun certainly does effect the Moon's orbit, but no so much its shape as other effects. Even the ancients (Ptolemy) noticed some of the effects. The Moon, for example, appears to speed up at new Moon and slow down at full Moon. This is the eviction, and Ptolemy saw this. There are lots of other effects, some rather small. The eviction is the largest effect.brainstorm said:Why wouldn't/isn't the sun's gravitational pull on the moon noticeable in its orbital shape?
That's interesting. Doesn't that mean that the Earth must be decelerating or accelerating in its path around the sun depending on where the moon is in its orbit?DaleSpam said:You are correct, the moon does go around the sun rather than the earth. The Earth just adds a wobble to the moon's path around the sun.
That is not what happens. There certainly is an effect, however. If the Sun and other planets were not present and if the Earth truly was spherical the Moon would follow an elliptical path. The line from the Moon at perigee to the Moon at apogee would be unchanging. What the Sun does is to make that line of apsides precess. It takes just under nine years for the Moon's line of apsides to complete one revolution.brainstorm said:Also, from the other posts it really sounds like the moon should be much closer to Earth when it's on the side opposite the sun.
The effect would be to change the Earth's perihelion and apihelion by a rather small amount, and opposite the sense that you have concluded.Here's another related question: if the moon would be annihilated as it is orbiting on the sun-side of the Earth, would that cause the Earth to move away from the sun? If so, how far would it go? What about if that happened while it were on the side away from the sun? Would Earth fall into the sun then?
D H said:The effect would be to change the Earth's perihelion and apihelion by a rather small amount, and opposite the sense that you have concluded.
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