Low Tide at Guernsey

The British Isles are known to have some of the wildest variations in tidal heights on Earth — note the stains on the seawall in St. Peter Port, Guernsey Island. Photo by the author

The British Isles are known to have some of the wildest variations in tidal heights on Earth — note the stains on the seawall in St. Peter Port, Guernsey Island. Photo by the author

Low Tide at Guernsey

It was the incomparable Isaac Newton who demonstrated that the gravitation of the Moon (and somewhat less, the gravitation of the Sun) created the tides on Earth.

The universal law of gravitation, formally introduced by Isaac Newton in his definitive treatise, “Philosophiae Naturalis Principia Mathematica” (“Mathematical Principles of Natural Philosophy,” 1687), explained that the force between two bodies is proportional to the product of their masses and inversely proportional to the square of their separation. Because of the immense disparity in the masses of the Sun and Moon (a ratio of 27 million) and in spite of the inverse square of the inverse of their relative distances squared (1/395^2), the Sun-Earth attraction is 174 times greater than the Moon-Earth attraction.

However, two diametrically opposite locations on the Earth (i.e. the diameter of the earth) compared with the distance between the Sun and the Earth is a miniscule 0.000 043, whereas the same two diametrically opposite locations on the Earth compared with the distance between Moon and the Earth is 0.016 06. In light of these two figures, the Sun’s effect on Earthly tides compared with that of the Moon is approximately (0.016 06/0.000 043) x 174 = 0.46. The Sun’s effect is only 46% of the Moon’s.

The British Isles are known to have some of the wildest variations in tidal heights on Earth — note the stains on the seawall in St. Peter Port, Guernsey Island. Another area that sees such drastic difference in tides is the Bay of Fundy in Canada. Record differences between high and low tides of up to 15 —> Read More

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