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How fast is Earth? An update on the importance of the introduction of leap seconds to the time standard and its implications for atomic satellites and satellite navigation
• Now, Earth’s rotation seems to have accelerated, outpacing the time standard, and raising the possibility that an unprecedented ‘negative’ leap second might soon be required — a daunting prospect in a world reliant on consistent timekeeping.
The alignment is maintained with the addition of leap seconds to the official time standard because the rate of rotation on the planet varies.
In 1967, the internationally accepted definition of the second changed. The standard for measuring time was determined by a quantum transition between two states of a caesium atom. The change was motivated by accuracy: caesium atomic clocks keep time on the basis of the ultrastable frequency of the photons exchanged in the quantum transition. This seemed like a safer bet than Earth’s movements, which weren’t as regular as was first assumed.
Atomic clocks have enabled the development of great technologies, such as satellite navigation and, in an age of the global navigation satellite system (GNSS), celestial navigation is much less relevant than it was in 1972. The risk of failures is caused by the insertion of a leap second and the onboard atomic clock that regulates their timekeeping. Perhaps more importantly, the addition of leap seconds can have drastic effects on computer infrastructure in the increasingly connected modern world (see go.nature.com/44y88yp).
The CGPM resolution stipulates that the maximum difference between the two times (denoted ut1 − utc) will be increased in or before 2035, and that the details of the new maximum and how it is to be implemented will be decided at the next CGPM meeting in 2026 (see go.nature.com/3vqddy2). Most delegates support swift implementation of new rules, but others would prefer more time to modify their systems. The International Telecommunication Union regulates the transmission of time signals and endorsed the decisions at the World Radiocommunication Conference in a few years.
She says that the three year delay is positive, because even if there is still a negative second needed, it will be later than expected.
Although the individual contribution of each process is somewhat uncertain, their sum is known precisely: it has led to an increase in Earth’s rotation period of 6 millionths of a second per year4. The effect of this slowing is what causes the clock error. This error describes a discrepancy in the timing of eclipses: events recorded by ancient astronomers seem to have occurred at times that differ from those predicted by assuming that Earth’s rotation rate has remained unchanged since ancient times. Clock error increases with the age of the eclipse and reaches around 4 hours for eclipses that were observed 2,500 years ago5.
“We do not know how to cope with one second missing. Felicitas Arias, the former director of the Time Department at the International Bureau of Weights and Measures in Svres, France, said that this is the reason why time metrologists are worried.
It is hoped that some people will take action due to the influence of climate change on timekeeping. He says that he can worry about climate change without this, but it is another way of impressing on people how big a deal this is.
The introduction of a leap second, which gives Earth a second more time than the official time standard, has led to an increase in Earth’s rotation period by 6 millionths of a second per year, a study has found. The study suggested that Earth’s rotation rate has been increasing since ancient times, when it was believed that Earth’s rotation rate was unchanged.