Our Days Are a Smidge Longer Than They Used to Be
Which we know thanks to some meticulous ancient astronomers
By Elizabeth Armstrong Moore,  Newser Staff
Posted Dec 10, 2016 8:33 AM CST
This Sept. 13, 2015 image provided by NASA shows the moon, left, and the Earth, top, transiting the sun together, seen from the Solar Dynamics Observatory. This image was taken in extreme ultraviolet...   (NASA/SDO via AP)

(Newser) – The meticulous work of ancient astronomers has led to a modern observation: Our days are longer than they used to be. Not that you'd notice: The new research in the Proceedings of the Royal Society A shows that it takes the Earth a tiny bit longer these days to complete a single rotation than it did eons ago. It's the kind of stuff that's measured in milliseconds per century, but those milliseconds add up. Over the last 2,500 years or so, they'd total seven hours, which the Los Angeles Times puts this way: "If humanity had been measuring time with an atomic clock that started running back in 700 BC, today that clock would read 7 p.m. when the sun is directly overhead rather than noon." Maybe more remarkable is that the work is the result of a tireless 40-year investigation into ancient timekeeping records dating back 2,700 years.

Scientists led by Richard Stephenson of the UK's Durham University have been poring over Babylonian clay tablets, Chinese observations made through the use of water clocks, and Arab astronomical records ("superb") that tracked solar and lunar eclipses. "The most astounding thing about this paper is the fact that we have this information at all," a geophysicist not involved in the study tells the Times. Researchers are still hoping to find observations from the Incas and the Maya, and to fill in their largest hole between 200 and 600 AD, but they've measured the Earth's deceleration at 1.8 milliseconds per day per century. Given the moon's gravitational effect on our oceans, the revelation that Earth is decelerating isn't a surprise, notes the Christian Science Monitor, though astronomers had previously estimated a higher rate. (This atomic clock won't lose a second for 15 billion years.)

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