Roy Smith wrote: > Steven D'Aprano <[EMAIL PROTECTED]> wrote: > > >High and low tides aren't caused by the moon. > > > They're not???
Nope. They are mostly caused by the continents. If the Earth was completely covered by ocean, the difference between high and low tide would be about 10-14 inches. (Over deep ocean, far from shore, the difference is typically less than 18 inches.) The enormous difference between high and low tide measured near the shore (up to 45 feet in the Bay of Fundy in Canada, almost forty times larger) is caused by the interaction of the continents with the ocean. In effect, the water piles up against the shore, like in a giant bathtub when you slosh the water around. The true situation is that tides are caused by the interaction of the gravitational fields of the sun, the moon and the Earth, the rotation of the Earth, the physical properties of water, its salinity, the depth, shape and composition of the coast and shoreline, the prevailing ocean currents, vibrationary modes of the ocean (including up to 300 minor harmonics), ocean storms, and even the wind. You can understand why we usually simplify it to "the moon causes the tides", even though the moon isn't even the largest contributing factor. See, for example: http://home.hiwaay.net/~krcool/Astro/moon/moontides/ -- Steven -- http://mail.python.org/mailman/listinfo/python-list
