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posted by janrinok on Tuesday August 02, @12:10PM   Printer-friendly [Skip to comment(s)]
from the fleeting-milliseconds-slip-by dept.

Considering the recent thread on the potential removal of leap seconds, a story in TheAge aussie paper seemed worth adding to the discussion:

Earth had its shortest day since records began last month, with 1.59 milliseconds shaved off the usual 24 hour spin on June 29 - raising the prospect that a negative leap second may soon be needed to keep clocks matched up with the heavens.

The Earth appears to be spinning slightly faster than normal.

Usually, Earth's average rotational speed decreases slightly over time and timekeepers have been forced to add 27 leap seconds to atomic time since the 1970s as the planet slows.

But since 2020, the phenomenon has reversed with records being frequently broken over the last two years. The previous fastest day was -1.47 milliseconds under 24 hours on July 19 2020 and it was almost broken again on July 26, when the day was -1.50 milliseconds shorter. While the effect is too small to be noticeable by humans, it can accumulate over time, potentially impacting modern satellite communication and navigation systems which rely on time being consistent with the conventional positions of the Sun, Moon and stars.

It means that it may soon be necessary to remove time, adding a negative leap second, and speeding up global clocks for the first time ever.

Related stories:
  Why One Critical Second Can Wreak Havoc On The Internet
  5. 4. 3. 2. 1. 1... An Extra Second to See Out 2016


Original Submission

Related Stories

5. 4. 3. 2. 1. 1... An Extra Second to See Out 2016 39 comments

Phys.org (among many other sites) is reporting on a leap second being added before the end of 2016:

As if 2016 has not been long enough, the year's dying minute will last an extra second to make up for time lost to Earth's slowing rotation, timekeepers say.

Countries that use Coordinated Universal Time—several West African nations, Britain, Ireland and Iceland—will add the leap second during the midnight countdown to 2017—making the year's final minute 61 seconds long.

For others, the timing will be determined by the time zone they live in, relative to UTC.

"This extra second, or leap second, makes it possible to align astronomical time, which is irregular and determined by Earth's rotation, with UTC which is extremely stable and has been determined by atomic clocks since 1967," the Paris Observatory said in a statement.

The observatory houses the International Earth Rotation and Reference Systems Service (IERS), responsible for synchronising time.

"The sequence of dates of the UTC second markers will be: 2016 December 31 23h 59m 59s, 2016 December 31 23h 59m 60s, 2017 January 1, 0h 0m 0s," the IERS website states.

Here is the original IERS announcement. There have been times in the past when the addition of a leap-second caused havoc — it is non-trivial to update the clocks on all the systems in an organization at the same time. When activity "A" happens before activity "B", but because of inconsistent system clocks the timestamps imply otherwise, things can go sideways in a hurry.


Original Submission #1Original Submission #2

Why One Critical Second Can Wreak Havoc On The Internet 37 comments

Arthur T Knackerbracket has processed the following story:

Google, Microsoft, Meta and Amazon launched a public effort Monday to scrap the leap second, an occasional extra tick that keeps clocks in sync with the Earth's actual rotation. US and French timekeeping authorities concur.

Since 1972, the world's timekeeping authorities have added a leap second 27 times to the global clock known as the International Atomic Time (TAI). Instead of 23:59:59 changing to 0:0:0 at midnight, an extra 23:59:60 is tucked in. That causes a lot of indigestion for computers, which rely on a network of precise timekeeping servers to schedule events and to record the exact sequence of activities like adding data to a database.

The temporal tweak causes more problems -- like internet outages -- than benefits, they say. And dealing with leap seconds ultimately is futile, the group argues, since the Earth's rotational speed hasn't actually changed much historically.

"We are predicting that if we just stick to the TAI without leap second observation, we should be good for at least 2,000 years," research scientist Ahmad Byagowi of Facebook parent company Meta said via email. "Perhaps at that point we might need to consider a correction."

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  • (Score: 3, Interesting) by JoeMerchant on Tuesday August 02, @01:59PM (2 children)

    by JoeMerchant (3937) Subscriber Badge on Tuesday August 02, @01:59PM (#1264515)

    Water is heavy, moving water from the glaciers down to sea level is like the ice skater in a spin pulling in her arms...

    • (Score: 1) by shrewdsheep on Tuesday August 02, @04:36PM (1 child)

      by shrewdsheep (5215) on Tuesday August 02, @04:36PM (#1264577)

      Interesting thought. To nitpick a bit: it would also depend on the latitude of the glacier. A hypothetical glacier at the north pole would have orbital speed of zero. Assuming the water distributes evenly across the globe after melting (eventually) this glacier would slow earth down. Overall your point stands, I believe.

      • (Score: 2) by JoeMerchant on Tuesday August 02, @06:38PM

        by JoeMerchant (3937) Subscriber Badge on Tuesday August 02, @06:38PM (#1264625)

        Ummm... to pick another nit... I believe the earth is a bit squashed, fatter at the equator, so moving water from the pole to the equator might also slow the spin a bit, but floating ice probably doesn't have any net effect when it melts, since it is "pushing up" sea level by floating, no matter where it's floating.

  • (Score: 0) by Anonymous Coward on Tuesday August 02, @03:42PM (3 children)

    by Anonymous Coward on Tuesday August 02, @03:42PM (#1264550)

    Okay, so eventually at some point in the future this problem will likely have to be dealt with in better way. Eventually, the earth's rotational speed will begin to slow appreciably due to tidal forces, so that even the semi-annual "leap seconds" won't be enough to "correct" things. But that's a long-term issue, and we have no idea how things may change with timekeeping and how we conceptualize it if we begin more intensive space exploration, etc. in the next few centuries.

    For now, leap seconds are a "patch." Just like leap years are a "patch" that fixed a "bug" in the old Roman calendar. Then the Gregorian correction (skip leap years in years divisible by 100 but not divisible by 400) fixed the drifting "bug" a bit more. But it too will eventually not be enough to correct for drift of the equinoxes. That's far into the future, but the Gregorian system is a pretty good one, and not too terribly difficult to implement. (I say that, but how many systems are going to have issues with no leap year in the year 2100??)

    Anyhow, the issue leap seconds seem to be dealing with is also a kind of temporary patch that will work for a reasonable timespan into the future -- we don't want the official time to drift "too far" off the alignment with other celestial objects (although "too far" is definitely a subjective phrase). But we know (if our general understanding of long-term trends with gravity holds up) that the long-term trend should be toward slowing rotation for the earth, which means adding seconds occasionally.

    So why subtract ONE? Lots of code deals with positive leap seconds. Very little (from what I understand) accounts for the possibility of NEGATIVE leap seconds.

    If the earth's "speed up" trend continues for several years and we end up starting to accumulate a significant difference in that direction, maybe we either need to take action (actually do some negative leap seconds) or just give up on the exact synchronization of time of day with planetary rotation completely.

    I know there is a growing movement to abolish leap seconds entirely already, and I can see the argument for that both ways. It does make sense. But if we are going to have them, it makes sense to use them as corrections to stay on-course with the long-term trend, which (again, assuming we actually understand planetary rotation well) is going to require adding seconds.

    Suddenly turning around and subtracting a second just because one or two years were a few milliseconds off from the long-term trend would be like saying, "Hey, let's skip leap year in 2024 because springtime temperatures arrived a little earlier in 2022 and 2023!" That's not why we have leap years... leap day keeps us in sync with the overall trend, not the annual whims of the earth.

    Again, if our understanding of rotation starts to change in the coming decades, and rotational period really starts trending shorter for a significant period of time, then we need to change our thinking. But IF we're going to bother with leap seconds, at least let's use them to keep to the long-term trend.

    • (Score: 1) by aafcac on Tuesday August 02, @04:52PM

      by aafcac (17646) on Tuesday August 02, @04:52PM (#1264588)

      It already has, it just hasn't happened appreciably during the period of time when we had accurate and precise clocks. Since the earth formed, there have been days and even weeks worth of extra days added to the revolution as things slowed down.

    • (Score: 3, Informative) by Anonymous Coward on Tuesday August 02, @05:40PM

      by Anonymous Coward on Tuesday August 02, @05:40PM (#1264602)

      But we know (if our general understanding of long-term trends with gravity holds up) that the long-term trend should be toward slowing rotation for the earth, which means adding seconds occasionally.

      So why subtract ONE? Lots of code deals with positive leap seconds. Very little (from what I understand) accounts for the possibility of NEGATIVE leap seconds.

      If the earth's "speed up" trend continues for several years and we end up starting to accumulate a significant difference in that direction, maybe we either need to take action (actually do some negative leap seconds) ...

      But if we are going to have them, it makes sense to use them as corrections to stay on-course with the long-term trend, which (again, assuming we actually understand planetary rotation well) is going to require adding seconds.

      This is basically how the process already works.

      UTC is (currently) specified to be within ±0.9 seconds of UT1. To achieve this, there are provisions for leap seconds in either direction. A negative leap second would only be inserted if the UT1-UTC difference is getting uncomfortably close to +0.9s

      As you mention, the overall trend is a slowing rotation (primarily due to tidal drag from the moon) so a negative leap second has literally never been observed to date.

      On the other hand, we have also never observed the difference going more positive year over year before. But the difference is still negative and rotational speedups would have to continue for many more years before we get close to +0.9s.

    • (Score: 3, Touché) by JoeMerchant on Tuesday August 02, @06:41PM

      by JoeMerchant (3937) Subscriber Badge on Tuesday August 02, @06:41PM (#1264627)

      Meanwhile, that giant comet plunging towards us from outside the orbital plane of the solar system is going to screw up all the other predictions when it hits...

  • (Score: 2) by darkfeline on Tuesday August 02, @10:27PM

    by darkfeline (1030) on Tuesday August 02, @10:27PM (#1264684) Homepage

    I'm sure it's due to all of the dead people spinning in their graves. Kids these days...

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