Dec 31 1976
From The Space Library
Clocks around the world would be set back one second this New Year's Eve, because the earth's spin was that much longer in 1976 than it was last year. The backward move would be the sixth in the last 5 yr because of a slowing in the earth's spin, the Washington Post explained; the changes were made twice in 1972 and once in each of the last 4 yr, each time on New Year's Eve. The standard U.S. timepiece (at the Natl. Bureau of Standards Laboratory at Boulder, Color) would be reset at midnight GMT (7 pm in Washington, D.C.), and similar atomic clocks would be reset at the same moment in more than 80 countries including the Soviet Union and the Peoples Republic of China. The earth's spin had been slowing for at least 250 yr, when it was first noticed, except for a 10-yr period before 1900 when the rotation speeder] up by 25 sec. In 1878, Simon Newcomb, then chief astronomer at the Naval Observatory, first systematically observed a fluctuation in the rate of rotation, which still is verified by 80 observatories around the world who send their findings to the Intl. Time Bureau in Paris, established in 1972 (the year the clocks lost 2 sec). Scientists attributed the slowdown to the moon's pull on the tides, braking the motion of the earth's mantle. (W Post, 31 Dec 76, A2)
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