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The timing of the eclipses from these descriptions, however, conflicts with calculations of when the eclipses should have occurred if tidal friction alone explained the slowdown of the planet's rotation. C., Morrison said, the discrepancy was about 7 hours between what the tablets reported and what calculations based on the tidal models would have predicted."That discrepancy is the measure of how much the Earth has been changing over this period of time," Morrison said.
That change in shape alters Earth's rotation, much as a figure skater can change the speed of a spin by drawing her or his arms in or throwing them out wide.
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6) in the journal Proceedings of the Royal Society A. relates to the end of the last ice age, Agnew said.
Calculating the Earth's rotation time down to less than a millisecond matters because that number says something about the way the very shape of the planet has changed, said Duncan Agnew, a geophysicist at the University of California, San Diego, who was not involved in the new study. The planet is like a memory-foam mattress, Agnew said, gradually rebounding as the ice retreats.
Changes in Earth's rotation since that time are probably mostly due to changes in the dynamics of the liquid-iron core deep in the center of the Earth, Agnew said.
Very little is known about this liquid core, so the measurements of its effect on the planet's spin are important for future research, he said.
However, measurements of this tidal effect suggest that the planet should be slowing in its rotation by 2.3 milliseconds per century, slightly more than the new research finds.
The difference between 2.3 milliseconds and 1.8 milliseconds over a century may seem trivial, said study researcher Leslie Morrison, who worked at the Royal Greenwich Observatory for nearly 40 years.
The new study is perhaps the most comprehensive effort yet, Morrison said, mostly because the ancient Babylonians were so good at keeping records. C., this civilization, located in what is now Iraq, was keeping records on clay tablets in a writing system called cuneiform.
When archaeologists discovered some of these tablets in Babylonian ruins in the 1800s, the language had been lost; it took decades to decipher those original tablets.
Fortunately for modern-day Earth scientists, some of these tablets happened to contain records of eclipses, particularly solar eclipses, when the moon moves between the sun and the Earth, casting a shadow on this planet.