Tides occur because the gravitational force between two bodies decreases with distance. Gravitation is the universal force of attraction between all matter. It holds astronomical bodies together and attracts different bodies toward each other. Because gravity tugs on nearby things more strongly than on distant things, the oceans closest to the Moon feel the greatest attraction to the Moon. Being fluid, these nearby oceans move upward in response to the Moon's pull, until there is a balance between the upward force from the Moon and the downward force from Earth. The high tide on the far side of the Earth occurs because these most distant oceans feel the least attraction to the Moon. In essence, they are left behind as the Moon pulls the other parts of Earth toward itself with greater force.
In 1897 George Darwin, son of Charles, suggested that tides are causing the Moon to spiral away from us. His hypothesis was confirmed in 1969 after the Apollo 12 astronauts placed corner reflectors (like the red and orange ones on a car) on the Moon. By firing lasers from Earth to the Moon, off the corner reflectors, and back again, astronomers measured the round-trip time and, hence, the distance to the Moon. Repeating the experiment over several years, they confirmed Darwin's prediction. The Moon is receding at 2 inches per year.
To understand why the Moon is fleeing from us, imagine for a moment that neither Earth nor Moon rotated and that the Sun's tidal effect could be ignored. In this case, one of the two high ocean tides would be directly between Earth and Moon, while the other would be on the opposite side of Earth from the Moon
HM -- Please DO NOT PLAGIARIZE!
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