The world definitely wanted to end 2020 as soon as possible. This year, the Earth’s rotation has accelerated: 28 days were shorter than the previous record, set in 2005, according to British scientists from the National Physical Laboratory, initially cited by the media The Telegraph. A record was even broken on July 19, 2020 with a rotation of 1.40602 milliseconds less than the reference time, or 86.400 seconds (or 24 hours).
A gap between atomic time and universal time
Thanks to increasingly precise measurements by satellites, we have known for a long time that the Earth’s days are not regular: the rotation of the blue planet never lasts exactly 24 hours. It can vary cyclically by milliseconds due to several factors: movements of the oceans, attraction of the Moon, impact of the inner core.
These disturbances are not taken into account by the International Atomic Time, measured by atomic clocks, therefore a stable time and used as a reference: 86,400 seconds for a rotation. In contrast to universal time (UT) based on the rotation of the earth, calculated using astronomy.
“Leap seconds” to “catch up”
When the difference between the two is too important, the International Service of Earth Rotation and Reference Systems (IERS) decides to add a “leap second” either on June 30 or December 31 at midnight. The dial thus indicates 23:59:60, the atomic clocks stop one second to “catch up the delay”. An operation already carried out 27 times since the 1970s.
The newspaper Release take the example of the year 1987: the Earth had taken 497 milliseconds more, after calculating the sum of the annual deviations, to perform its rotations than if it had rotated while respecting the 86,400 seconds of reference. For the first time, one of those leap seconds could be removed due to the acceleration of the Earth’s rotation.