In 2020, the earth rotated so fast on its axis that the days were noticeably shorter. We may even soon have to set the clock back a forced tick to keep up with the rapid vortex.
It seems a bit contradictory. Where 2020 has felt to most people like a year that has dragged on endlessly from crisis to foreclosure and vice versa, the year has actually progressed at an all time high.
Or: the technology of time measurement anyway. After all, you and I won’t have noticed much of the millisecond time saving we booked last year. Yet this shorter Earth rotation time has been closely watched by the International Earth Rotation Reference Systems (IERS) Service, more than just a fun drink. It influences the setting of the “world clock” on which we all live, the global standard upon which all time zones are based.
Ultra-sensitive atomic clocks
This world time is also called UTC – not an abbreviation by the way, but a compromise between the English term CUT (Coordinated Universal Time) and the French term TUC (Temps Universel Coordonné). UTC, on the other hand, is based on international atomic time, which is tracked with 400 ultra-sensitive atomic clocks, located in 90 laboratories around the world.
“We have four of these clocks,” says Erik Dierikx, director of time at the VSL National Metrology Institute in Delft. There, he closely monitors data from the IERS, looking for when UTC begins to deviate too far from astronomical time.
While when we think of a day we quickly think of 24 hours, the actual duration of an orbit around the Earth’s axis differs slightly each day, according to data from the IERS. This has a natural cause: changes in wind, for example, or the flow of the oceans. Even the movements of the earth’s core have minimal influence on the speed of the Earth’s rotation.
“As soon as the difference between astronomical time and UTC becomes too large, a leap second is added,” explains Dierikx, who then programs such a second in atomic clocks with his colleagues. “The last leap of a second was added on January 1, 2017,” he says.
For decades, the Earth seemed to spin too slowly on average. But last year, things went fast, with remarkably short days. In fact, the shortest 28 days on the books since 1960 are all from 2020, the commerce website timeanddate.com recently reported. own analysis of IERS data. The most colorful did it on July 19, by (finished) a millisecond and a half less than 24 hours.
Second negative jump
And this year too, the earth is expected to rotate on its axis relatively quickly, reports the IERS in a prediction, so that astronomical time will continue to lag behind our clock time throughout the year in 2021.
Very cautiously, some time tourists are therefore even starting to think about introducing a negative leap second to put the clock back on line. Then we would get a minute of just 59 instead of 60 seconds, which evaporates a whole clock tick from the UTC books. This has never been done before.
“I think it will be some time before such a thing is necessary,” says Dierikx. “But in theory, it’s certainly possible. Our equipment can add seconds, but also erase. It would be a great unique opportunity.