Time doesnt have to be exactheres why

Date:
Sat, 31 Dec 2022 16:00:00 +0000

Description:
Starting in 2035, we'll be shaving a second off our New Year's countdowns. Hector Achautla The recent decision to axe the leap second shouldn't affect your countdowns or timekeeping too much. The post Time doesnt have to be exactheres why appeared first on Popular Science .

FULL STORY ======================================================================
Starting in 2035, we'll be shaving a second off our New Year's countdowns. Hector Achautla

Its official: The leap seconds time is numbered .

By 2035, computers around the world will have one less cause for glitching based on human time. Schoolchildren will have one less confusing calculation to learn when memorizing the calendar.

Our days are continually changing: Tiny differences in the Earths rotation build up over months or years. To compensate, every so often, authorities of world time insert an extra second to bring the day back in line. Since 1972, when the system was introduced, weve experienced 27 such leap seconds .

But the leap second has always represented a deeper discrepancy. Our idea of
a day is based on how fast the Earth spins ; yet we define the secondthe actual base unit of time as far as scientists, computers, and the like are concernedwith the help of atoms. Its a definitive gap that puts astronomy and atomic physics at odds with each other.

[Related: Refining the clocks second takes timeand lasers ]

Last month, the guardians of global standard time chose atomic physics over astronomy and according to experts, thats fine.

We will never abandon the idea that timekeeping is regulated by the Earths rotation. [But] the fact is we dont want it to be strictly regulated by the Earths rotation, says Patrizia Tavella , a timekeeper at the International Bureau of Weights and Measures (BIPM) in Paris, a multigovernmental agency that, amongst other things, binds together nations official clocks.

The day is a rather odd unit of time. We usually think about it as the duration the Earth takes to complete one rotation about its axis: a number from astronomy. The problem is that the worlds most basic unit of time is not the day, but the second, which is measured by something far more miniscule: the cesium-133 atom, an isotope of the 55th element.

As cesium-133s nucleus experiences tiny shifts in energy, it releases photons with very predictable timing. Since 1967, atomic clocks have counted
precisely 9,192,631,770 of these time-units in every second. So, as far as metrologists (people who study measurement itself) are concerned, a single
day is 86,400 of those seconds.

Except a day isnt always exactly 86,400 seconds, because the worlds revolutions arent constant .

Subtle motions, such as the moons tidal pull or the planets mass distribution shifting as its melty innards churn about, affect Earths spin. Some
scientists even believe that a warming climate could shuffle heated air and melted water closer to the poles, which might speed up the rotation .
Whatever the cause, it leads to millisecond differences in day length over
the year that are unacceptable for todays ultra-punctual timekeepers. Which
is why they try to adjust for it.

The International Earth Rotation and Space Systems Service (IERS), a scientific nonprofit responsible for setting global time standards, publishes regular counts of just how large the difference is for the benefit of the worlds timekeepers. For most of December, Earths rotation has been between 15 and 20 milliseconds off the atomic-clock day.

Scientists thinkit will take about a century for the difference to build up
to a minute. It will take about five millennia for it to build up to an hour.

Whenever that gap has gotten too large, IERS invokes the commandment of the leap second. Every January and July, the organization publishes a judgement
on whether a leap second is in order . If one is necessary, the worlds timekeepers tack a 61st second onto the last minute of June 30 or December
31, depending on whichever comes next. But this November, the BIPM ruled that by 2035, the masters of the worlds clocks will shelve the leap second in
favor of a still-undecided approach.

That means the Royal Observatory in Greenwich, Londonthe baseline for Greenwich Mean Time (GMT) and its modern successor, Universal Coordinated
Time (UTC)will drift out of sync with the days it once defined. Amateur astronomers might complain, too, as without the leap second, star sightings could become less predictable in the night sky.

But for most people, the leap second is an insignificant curiosityespecially compared to the maze of time zones that long-distance travelers face, or the shifts that humans must observe twice a year if they live in countries that observe daylight savings or summer time .

On the other hand, adding a subtle second to shove the day into perfect alignment comes at a cost: technical glitches and nightmares for programmers who must already deal with different countries hodgepodge of timekeeping. The absence of leap seconds will make things a little easier by removing the need for the occasional adjustment, but the difference will not be noticed by everyday users, says Judah Levine , a timekeeper at the National Institute of Standards and Technology (NIST) in Boulder, Colorado, the US government
agency that sets the countrys official clocks.

[Related: Its never too late to learn to be on time ]

The new plan stipulates that in 2026, BIPM and related groups will meet again to determine how much they can let the discrepancy grow before the guardians of time need to take action. We will have to propose the new tolerance, which could be one minute, one hour, or infinite, says Tavella. Theyll also propose how often they (or their successors) will revise the number.

Its not a decision that needs to be made right away. Its probably not necessary to reconcile atomic time with astronomical time, says Elizabeth Donley , a timekeeper at NIST. User groups that need to know time for astronomy and navigation can already look up the difference.

We cant currently predict the vagaries of Earths rotation, but scientists thinkit will take about a century for the difference to build up to a minute. Hardly anyone will notice, says Donley. It will take about five millennia for it to build up to an hour.

In other words, we could just kick the conundrum of counting time down the road for our grandchildren or great-grandchildren to solve. Maybe in the future, there will be better knowledge of the Earths movement, says Tavella, And maybe, another better solution will be proposed.

The post Time doesnt have to be exactheres why appeared first on Popular Science . Articles may contain affiliate links which enable us to share in
the revenue of any purchases made.



======================================================================
Link to news story:
https://www.popsci.com/science/leap-second-day-length/


--- Mystic BBS v1.12 A47 (Linux/64)
* Origin: tqwNet Science News (1337:1/100)