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Oracle bone shows a once-shorter day.

Oracle bone shows a once-shorter day

"Three flames ate the sun. Big stars [seen]."

These cryptic words, inscribed in Chinese characters on an ancient piece of tortoise shell, record a total solar eclipse in which the sun's corona and its streamers became visible and stars appeared in the sky. They also give a way of determining the Earth's rotation rate thousands of years ago.

In an ingenious piece of astronomical and historical detective work, Kevin D. Pang of the Jet Propulsion Laboratory in Pasadena, Calif., and his collaborators pinpointed the eclipse date: June 5, 1302 B.C. In turn, they deduced that a day is now 0.047 second longer.

"With such an analysis, we can get a better idea of how much the Earth's rotation rate varied in antiquity," Pang says. He described his team's findings this week at an American Astronomical Society meeting in Ann Arbor, Mich.

Before the invention of paper, scholars in ancient China wrote predictions and recorded events, including eclipses, on fragments of bone and tortoise shell known as oracle bones. Pang and his colleagues studied one particular eclipse record. By using computers to calculate the dates and paths of solar eclipses visible in China during a certain period of the Shang dynasty, they found two candidates that appeared to fit the oracle-bone data.

The team then turned to records of five lunar eclipses during the same period of Chinese history. After establishing that the Chinese day, as recorded in the oracle bone, started at roughly 3 a.m., the researchers found a pattern of lunar-eclipse dates that fits the date of one solar eclipse but not the other. At the same time, because any changes in the Earth's rotation rate would shift an eclipse's path from where it occurred, they worked out how much the length of the day had changed.
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Author:Peterson, I.
Publication:Science News
Date:Jun 17, 1989
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