MadSci Network: Astronomy

Re: Tides, why are they more influenced by the moon than the sun?

Area: Astronomy
Posted By: Phil Plait, MadSci Admin
Date: Wed May 28 12:47:53 1997
Area of science: Astronomy
ID: 864694900.As

The answer you got is correct; the tides from the Moon are larger because it is closer. Tides are caused by the change in gravity as you get closer to or farther from an object. You probably already know that as you get further from an object, the force you feel from gravity decreases. So someone standing on the side of the Earth nearer the Moon feels more gravity from the Moon than a person standing on the opposite side of the Earth. The difference between these two forces is what we call the "tidal force".

Gravity also depends on the mass of the object doing the pulling. The Sun is tremendously more massive than the Moon, but is also much farther away. Out here at the Earth, the numbers work out so that the tides from the Moon, which is smaller but closer, are about twice as strong as the tides from the Sun, which is more massive but farther away.

I have a more detailed explanation of this (along with a lot of other effects of tides) on my homepage. click here to see that page.

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