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Anonymous asked in Science & MathematicsAstronomy & Space · 9 years ago

# How would two moons affect tides on earth?

Suppose that Earth had two moons instead of one long ago. Would tides on Earth have been

larger, smaller, or the same during periods when the two moons were on the same side of Earth?

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As it is, our tides are caused by the moon and the sun together. The sun is farther away so has less influence, the moon has more influence. But when the moon and sun are both on the same side of earth, their gravities add and tides are stronger. When theyy are on opposite sides, their gravities cancel each other out and the tides are less. Every month tides get higher and higher for two weeks, then lower and lower for two weeks as the sun and moon go into and out of phase.

With two moons, you'd have three gravities either adding or subtracting, so the tides would be a lot more complicated. At some times the moons would be togehter in the sky and the tides would be a lot stronger. Other times the moons would oppose each other and cancel each other out. And you'd still have the sun exerting its influence.

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• Well lets explain it more technically for you .. The orbit of Earth's Moon is not exactly circular around the Earth , so the gravitational pull of Moon will vary along its orbit. Now Gravitational Force is a Vector , which means it has both Magnitude and Direction. Hence we have to take components ) F = mgsin A , mgcos (90 - A ) to under the residual effect or rather the effective force exerted by the 2 moon system if it were to exist. Now as per Newton's Law of Gravitation we need to take into consideration Masses and radius of the mass while calculating force of gravity and also we have to consider Theory of relativity also here since all are masses are moving that means the calculation become really complex. Hope it helps you to further think on this and conceptualize .. Take care

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• If we added a moon to the Earth-moon system, then when the 2nd moon was on the same side of Earth, the effect of it's gravity would be added to the moon's gravity, and would've enhanced the tides on Earth.

On a similar note, if they were 90 degrees in opposition, then the moon's tidal effect would've been reduced by the 2nd moon.

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• You can already think of it that way actually. Consider the Sun to be a moon of Earth for the purposes of tides, and you can see exactly what happens.

We have "spring tides" and "neap tides". when the sun either reinforces or fails to reinforce the lunar tide.

http://www.almanac.com/content/spring-tides-neap-t... (reasonable explanation of spring and neap)

If we had a second moon, the two moons would at times reinforce, and at times cancel, or become negligible. If we had a second moon the size of our first moon.... wow.. that would be some good surfing when they lined up.

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