Earth’s Day Lengthens By Two Milliseconds a Century, Astronomers Find

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Researchers at Durham University and the UK’s Nautical Almanac Office compiled nearly 3, 000 years of celestial records and found that with every passing century, the day on Earth lengthens by two milliseconds as the planet’s rotation gradually winds down. The Guardian reports: The split second gained since the first world war may not seem much, but the time it takes for a sunbeam to travel 600km towards Earth can cost an Olympic gold medal, as the American Tim McKee found out when he lost to Sweden’s Gunnar Larsson in 1972. For those holding out for a whole extra hour a day, be prepared for a long wait. Barring any change in the rate of slowing down, an Earth day will not last 25 hours for about two million centuries more. Researchers at Durham University and the UK’s Nautical Almanac Office gathered historical accounts of eclipses and other celestial events from 720BC to 2015. The oldest records came from Babylonian clay tablets written in cuneiform, with more added from ancient Greek texts, such as Ptolemy’s 2nd century Almagest, and scripts from China, medieval Europe and the Arab dominions. The ancient records captured the times and places that people witnessed various stages of solar and lunar eclipses, while documents from 1600AD onwards described lunar occultations, when the moon passed in front of particular stars and blocked them from view. To find out how the Earth’s rotation has varied over the 2, 735-year-long period, the researchers compared the historical records with a computer model that calculated where and when people would have seen past events if Earth’s spin had remained constant. The astronomers found that Earth’s spin would have slowed down even more had it not been for a counteracting process. Since the end of the most recent ice age, land masses that were once buried under slabs of frozen water have been unloaded and sprung back into place. The shift caused the Earth to be less oblate — or squished — on its axis. And just as a spinning ice skater speeds up when she pulls in her arms, so the Earth spins faster when its poles are less compressed. Changes in the world’s sea levels and electromagnetic forces between Earth’s core and its rocky mantle had effects on Earth’s spin too, according to the scientists’ report in Proceedings of the Royal Society. Read more of this story at Slashdot.

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Earth’s Day Lengthens By Two Milliseconds a Century, Astronomers Find

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