Credit: NASA
Compensating for the lost time may prove challenging for scientists, says Astronomy magazine. Turning the internet clock back one second implies a repeat of a computer-generated timestamp for example, which might confuse some vital systems not designed to handle that.
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Ever feel like there’s just not enough time in the day? Turns out, you might be onto something.
Earth is rotating faster than it has in the last half-century, resulting in our days being ever-so-slightly shorter than we’re used to.
And while it’s an infinitesimally small difference, it’s become a big headache for physicists, computer programmers and even stockbrokers.
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“As time goes on, there is a gradual divergence between the time of atomic clocks and the time measured by astronomy, that is, by the position of Earth or the moon and stars,” says Judah Levine, a physicist in the time and frequency division of the National Institute of Standards and Technology.
Basically, a year as recorded by atomic clocks was a bit faster than that same year calculated from Earth’s movement. “In order to keep that divergence from getting too big, in 1972, the decision was made to periodically add leap seconds to atomic clocks,” Levine says.
Leap seconds work a little like the leap days that we tack on to the end of February every four years to make up for the fact that it really takes around 365.25 days for Earth to orbit the Sun. But unlike leap years, which come steadily every four years, leap seconds are unpredictable.
The International Earth Rotation and Reference Systems Service keeps tabs on how quickly the planet spins by sending laser beams to satellites to measure their movement, along with other techniques.
When the time plotted by Earth’s movement approaches one second out of sync with the time measured by atomic clocks, scientists around the world coordinate to stop atomic clocks for exactly one second, at 11:59:59 pm on June 30 or December 31, to allow astronomical clocks to catch up. Voila — a leap second.
Unexpected change
Since the first leap second was added in 1972, scientists have added leap seconds every few years. They’re added irregularly because Earth’s rotation is erratic, with intermittent periods of speeding up and slowing down that interrupt the planet’s millions-of-years-long gradual slowdown.
“The rotation rate of Earth is a complicated business. It has to do with exchange of angular momentum between Earth and the atmosphere and the effects of the ocean and the effect of the moon,” Levine says. “You’re not able to predict what’s going to happen very far in the future.”
But in the past decade or so, Earth’s rotational slowdown has … well, slowed down. There hasn’t been a leap second added since 2016, and our planet is currently spinning faster than it has in half a century.
Scientists aren’t sure why.
“This lack of the need for leap seconds was not predicted,” Levine says. “The assumption was, in fact, that Earth would continue to slow down and leap seconds would continue to be needed. And so this effect, this result, is very surprising.”
The trouble with leap seconds
Depending on how much Earth’s rotations speed up and how long that trend continues, scientists might have to take action. “There is this concern at the moment that if Earth’s rotation rate increases further that we might need to have what’s called a negative leap second,” Whibberley says. “In other words, instead of inserting an extra second to allow Earth to catch up, we have to take out a second from the atomic timescale to bring it back into state with Earth.”
But a negative leap second would present scientists with a whole new set of challenges. “There’s never been a negative leap second before and the concern is that software that would have to handle that has never been tested operationally before,” Whibberley adds.
Full article here.
via Tallbloke’s Talkshop
February 3, 2022 at 10:54AM
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