To the run of men, the earth seems to rotate with trustworthy steadiness. Astronomers know better. Observed with their sharp-eyed instruments, the earth's rotation is a wobbly business. In Nature, Astronomer T. Gold of Britain's Royal Greenwich Observatory tells how he took the wobble apart and used it to show, among other things, how Antarctica may have got its deposits of coal.
Most of the earth's wobbling is a grand motion that makes its axis describe a 23° cone once every 26,000 years. This precession is caused by the pull of the sun...
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