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How the leap second is tied to day length

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Formula: Leap seconds are counted.

By 2035, computers around the world will have one less source of glitches based on human time. Schoolchildren no longer need to learn one complicated calculation when memorizing a calendar.

Our days are constantly changing. Small differences in the rotation of the Earth add up over months or years. To compensate for this, the world time keeper often inserts an extra second and he puts the day back. Since the introduction of the system in 1972, 27 leap seconds.

But leap seconds always represent a deeper discrepancy. Our His day is based on the rotation speed of the Earth. But we define his second. actual The basic unit of time, with the help of atoms, as far as scientists, computers, etc. are concerned. This is the critical gap that pits astronomy and nuclear physics against each other.

[Related: Refining the clock’s second takes time—and lasers]

Guardians of Universal Time last month chose nuclear physics over astronomy— Experts say that’s fine.

“We never give up on the idea that timekeeping is regulated by the rotation of the Earth. [But] the fact is we don’t want it Strictly It is regulated by the rotation of the earth.” Patrizia Taverathe timekeeper of the Paris International Bureau for Weights and Measures (BIPM), a multi-governmental body that unites the official clocks of different countries, among other things.

A day is a rather strange unit of time. We usually think of it as the time it takes for the Earth to make one revolution of her around its axis. This is a number from astronomy. The problem is that the most basic unit of time in the world is not his day, but a much smaller unit, the second. Cesium-133 atom, the isotope of the 55th element.

The nuclei of cesium-133 emit photons with very predictable timing due to small changes in energy. Since 1967, atomic clocks have accurately counted 9,192,631,770 of these time units per second. So as far as metrologists (those who study the measurements themselves) are concerned, a day is 86,400 seconds.

However, because the rotation of the world is not constant, a day is not always exactly 86,400 seconds.

Subtle movements such as the moon’s tidal forces and changes in the mass distribution of the planet as its molten interior moves about affect the Earth’s rotation. Some scientists believe that as the climate warms, heated air and melted water could move closer to the poles. speed up rotationWhatever the cause, it leads to millisecond differences in day length over the year, which is unacceptable for today’s ultra-punctual timekeepers.

The International Earth Rotating Space Systems Service (IERS) is a scientific non-profit organization responsible for setting the global time reference. Issue a periodic count About how big the difference is, for the benefit of the world’s timekeepers. During most of December, the Earth’s rotation is 15 to 20 milliseconds off the atomic clock day.

Scientists believe it would take about a century for the difference to reach a minute. It takes about 5000 years for it to become an hour.

When that gap becomes too large, IERS invokes a leap second order. In January and July of each year, the organization publishes the following verdicts: Whether leap seconds are appropriateAs appropriate, world timekeepers add 61 seconds to the last minute on June 30th or December 31st. However, in November of this year, the BIPM decided that by his 2035, the world’s watch experts would shelve leap seconds and adopt an approach that has yet to be decided.

This means that the Royal Observatory in Greenwich, London (the baseline for Greenwich Mean Time (GMT) and its successor, Coordinated Universal Time (UTC)) will be out of sync with the date as it was once defined. Even amateur astronomers might complain if there were no leap seconds. Star sightings can be difficult to predict in the night sky.

But for most people, leap seconds are a minor curiosity. Especially when compared to the maze of time zones a long-distance traveler faces and the changes humans have to observe her twice a year if they live in a country that adopts daylight saving time or daylight saving time.

On the other hand, adding subtle seconds to perfectly match a day comes at a price. It’s a technical glitch and a nightmare for programmers who have to deal with a hodgepodge of timekeeping from different countries. “The lack of leap seconds makes it a little easier because you don’t have to make occasional adjustments, but everyday users won’t notice the difference,” he said. Judah LevineIt is the timekeeper of the National Institute of Standards and Technology (NIST) in Boulder, Colorado, the United States government agency that sets the nation’s official clock.

[Related: It’s never too late to learn to be on time]

The new plan stipulates that the BIPM and related groups will meet again in 2026 to determine how far this disagreement can be escalated before the Guardians of Time take action. “We need to propose new tolerances of one minute, one hour, or infinity,” he says Tavella. He also suggests how often they (or their successors) will revise the numbers.

It’s not a decision you have to make right away.Says it’s “probably not necessary” to match atomic and astronomical time Elizabeth Donley, the NIST timekeeper. “User groups who need to know the time for astronomy or navigation can already see the difference.”

Although it is not possible to predict the vagaries of the Earth’s rotation today, scientists believe it will take about a century for the difference to be one minute. “No one will notice,” he says Donley. It takes about 5000 years for it to become an hour.

In other words, we can kick off the conundrum of counting how long it will take our grandchildren and great-grandchildren to solve. A better solution may be suggested,” says Tabera.

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