Ancient eclipse records show that days on Earth are getting just a little longer

A report published in Proceedings of the Royal Society A found that a single rotation of Earth on its axis has slowed by 1.8 milliseconds per century. Thanks to hundreds of records of lunar and solar eclipses carved in clay tablets and written into dynastic histories, modern scientists have determined that the speed at which Earth spins on its axis has slowed by 1.8 milliseconds per day over the course of a century, according to a report published Wednesday in the journal Proceedings of the Royal Society A. For the record: A previous version of this story said the time it takes for Earth to complete a single rotation on its axis had slowed by 1.8 milliseconds per century. “There is time and then there is how fast the Earth spins,” said Duncan Agnew, a geophysicist at Scripps Institution of Oceanography in San Diego, who was not involved with the work. In our modern world, governed by atomic clocks, the International Earth Rotation and Reference Systems Service calls for a leap second to be added whenever Universal Time is on track to be out of sync with Terrestrial Time by more than 0.9 of a second.