We have known for a long time that Earth's days are slowly but surely getting longer due to our planet's interactions with the Moon, but a new analysis suggests that the increase in length is less than previous estimates. This suggests more mechanisms are at play.
A team of British researchers estimated that the day is slowing by 1.8 milliseconds per century, slower than the previous estimate of 2.3 milliseconds, which was based on the effect of the tides on Earth. The findings are published in the Proceedings of the Royal Society A.
The new estimate tells us that it will take 6.7 million years before we need to add one minute to the length of the average day. Although this change is clearly minimal, the difference in the length of any day (not the average) varies not insignificantly, and that’s why timekeepers worldwide since 1972 have added the odd leap second to our calendars, matching the changes in rotation to the accurate time shown by atomic clocks.
The team used records of eclipses from Babylonian, Greek, and Chinese astronomers, as well as observations taken by Arab and Medieval scholars, to make their findings. They also used astronomical data of the Moon passing in front of stars from 1600 CE to today.
The researchers found discrepancies between where the eclipse should have been observable (modeled using sophisticated software) and where it was actually seen on Earth according to the records. From this, they were able to extrapolate how different Earth’s rotation must have been.
All this information provides a picture of changes in the length of Earth's day that span 27 centuries. The results suggest that there are fluctuations in the slowing down rate, some over decades and others over centuries.
The causes of these uncertainties are found deep within Earth. The interaction between the conducting regions of the mantle and the magnetic field from the core affect Earth’s overall rotation. And even changes in ice distribution affects the speed of our planet. The shrinking of the ice caps since the last ice age has changed the shape of our planet.
And if you're sick of 2016, there's more bad news, as it will be one of those longer years with one second being added on December 31 at midnight.