Why Time Will Stop For a Leap Second

National Geographic ^ | June 26, 2015 UTC | Jane J. Lee

[Lonesome in Massachussets]

Just as leap years keep our calendars lined up with Earth's revolution around the sun, leap seconds adjust for Earth's rotation. This kind of fine-tuning wasn't much of an issue before the invention of atomic clocks, whose ticks are defined by the cycling of atoms. Cesium-based clocks, one kind of atomic clock, measure the passage of time much more precisely than those based on the rotation of our planet, so adding a leap second allows astronomical time to catch up to atomic time.

Most of us won't notice the addition, which happens at 23:59:59 coordinated universal time (UTC), or 7:59 p.m. ET, unless we deal in timescales shorter than a second, or if we use a computer program that crashes because it can't handle the leap second. It's happened before: The 2012 leap second brought down Reddit, Gawker Media, and Mozilla.

Picture of clocks The reflection of clocks and lights streak a window in Prague in the Czech Republic. PHOTOGRAPH BY ABRAHAM NOWITZ, NATIONAL GEOGRAPHIC CREATIVE "It's a major interruption mostly because there are a lot of systems that aren't prepared to handle the leap second correctly," says Judah Levine, a physicist at the National Institute of Standards and Technology (NIST) in Boulder, Colorado. Leap seconds occur irregularly, which makes it hard for programmers to test their fixes, he explains.

Adding Time Leap seconds don't come on a regular schedule because Earth's rotation varies, says Demetrios Matsakis, chief scientist for time services with the United States Naval Observatory in Washington D.C. Our planet is slowing down, but it does so in unpredictable ways. So some periods require more leap seconds than others.

[Lonesome in Massachussets]

So researchers added ten seconds all at once in 1972 to the world's astronomical clocks, [Johnston,]explains. Inaccurately. Actually, UTC was set approximately equal to UT2 (a smoothed version of UT1) in 1958, and continuous adjustments had been made to civil time to keep it close to UT1 (time determined by earth's rotation) all along. Leaps, or discontinuities in civil time were made in multiples of 50 nanoseconds and the rate of UTC was slowed down by multiples of 15 parts per billion, to keep step with UT1. In 1972, the decision was made to bite the bullet, and allow UTC to "beat" atomic seconds, adding or removing a leap second as needed to stay with 0.9 seconds of UT1.

[Cicero]

The 2012 leap second brought down Reddit, Gawker Media, and Mozilla.

I won't cry if it does it again. Maybe this time Gawker will stay down.

[SunkenCiv]

Thanks Lonesome in Massachussets.

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[PistolPaknMama]

So do we set our clocks backward or forward? /snort

[NonValueAdded]

Your clock will be one second fast as of 8 PM EDT in June 30th. So you would set it back. And those corporate slave masters will get one second of extra uncompensated labor out of the exploited masses on second shift. Watch for widespread demonstrations.

[ctdonath2]

I just want too see my Watch say 7:59:60.

[PistolPaknMama]

Watch for widespread demonstrations.

After this week, things are speeding to a head. This will drive the masses over the edge.

[Lonesome in Massachussets]

Back one second at June 30, 2015 23:59:60 (sic)

[garyb]

time.is promises to display 7:59:60 June 30th Eastern Time.

[NonValueAdded]

June 30th. You are a bit premature.

[Rodamala]

Not one mention of Global Warming in any of that. I can’t believe it.

[Lonesome in Massachussets]

Global warming is not completely absent. Current theory (and admittedly it is a weakly verified theory) holds that the current secular deceleration of the length of day caused by tidal friction should be more rapid, but is partially offset by the continued melting of the polar ice caps since the last ice age.

[Larry Lucido]

Can’t we just speed the earth up by a second?

[Lonesome in Massachussets]

The slowing of the earth is caused by tidal friction with the moon. Currently, the rate of loss of rotational kinetic energy is about one gigawatt. To maintain our current speed, which loses a second every 18 months would require a gigawatt on average, until, literally, the end of time. To speed up enough so that we would stop losing time, would require an additional one time investment of 200 gigawatt-years, spread over as long a period as desirable.

The mechanism for delivering the extra momentum is not clear to me. Perhaps vast arrays of west facing mirrors which would reflect solar radiation only in the westerly direction. Solar radiation pressure is about 9 micronewtons per meter-squared at the surface of the earth. I leave it to you to figure out how large an array of mirrors would be required.

Alternately, we could just adjust our watches every 18 months or so.

[Bloody Sam Roberts]

It won't. We're ready for it this time. There is an easy fix that can be put in place before June 30th. It involves setting up the Linux OS to restart the NTP daemon in slew mode 25-39 hours before the Leap Second occurrence.
Some time after the Leap Second occurs the NTP daemon is restarted in default mode.

[M Kehoe]

Good afternoon. I hope you are doing well.

Fwiw, I am not participating in this manipulation of time. I will remain one second behind.

5.56mm

[Lonesome in Massachussets]

You’re too late. UTC is already 35 seconds behind atomic time. Why would you prefer arbitrary atomic time, over more natural solar time. If we had invented atomic time in 136 BC, you’d be about two hours behind solar time by now.