Re: OT - Dinosaur Extinction Explained

jadel wrote:
On Jul 7, 7:54 am, jadel <delco...@xxxxxxxxxxx> wrote:
On Jul 6, 8:22 pm, "Les Stewart" <n...@xxxxxxxxxxxxxx> wrote:

It has always been thought the sun, earth & moon all move regularly and that
distance between them is stable.
Not any more! It is now known that the moon is moving away from the earth by
about 2 inches a year.
Old news.


Here's a correction and an explanation.

It was the acutually Apollo 12 mission that put the laser retro-
reflector on the moon.

The moon's recession from the earth was first postulated in 1897 when
Sir George Darwin, son of Charles Darwin, pointed out that the Earth-
Moon system had to obey the law of the conservation of angular
momentum. The moon has been spiraling away from the Earth since the
day the moon formed.

The rate of recession isn't constant. Conservation of angular momentum comes into the picture because tidal effects dissipate energy. This caused the moon to stop rotating about its axis and always present the same side to the earth. Although the moon's rotational energy was dissipated, its angular momentum can't be. Its angular momentum is greater at greater distance from the earth, so the former momentum of rotation, becoming momentum of revolution, implies greater distance.

The process continues because the moon's tidal effect on the earth is slowing the earth's rotation, dissipating energy but not momentum. (The days are getting longer.) Separation will stop increasing when the moon remains directly overhead at one place on earth.

Jerry
--
Engineering is the art of making what you want from things you can get.
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