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posted by cmn32480 on Friday December 30 2016, @05:08PM   Printer-friendly
from the like-this-year-hasn't-been-long-enough dept.

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

 
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  • (Score: 2) by martyb on Friday December 30 2016, @07:06PM

    by martyb (76) Subscriber Badge on Friday December 30 2016, @07:06PM (#447557) Journal

    So, it seems that we always are adding seconds - shouldn't we just recalibrate time so that we don't need to add or take away seconds for a long-ish period? If we can predict where the earth's rotation is going for the next 100 years, we could calibrate time to run a little ahead astronomically for a few years, then fall back, rinse, lather, repeat.

    Again, seems simple, doesn't it?

    Look again at the Wikipedia article on the leap second [wikipedia.org], paying special attention to the section Slowing rotation of the Earth [wikipedia.org]:

    Leap seconds are irregularly spaced because the Earth's rotation speed changes irregularly. Indeed, the Earth's rotation is quite unpredictable in the long term, which explains why leap seconds are announced only six months in advance.

    [...] The main reason for the slowing down of the Earth's rotation is tidal friction, which alone would lengthen the day by 2.3 ms/century.[14] Other contributing factors are the movement of the Earth's crust relative to its core, changes in mantle convection, and any other events or processes that cause a significant redistribution of mass. These processes change the Earth's moment of inertia, affecting the rate of rotation due to conservation of angular momentum, sometimes increasing earth's rotational speed (decreasing the solar day and opposing tidal friction). For example, glacial rebound shortens the solar day by 0.6 ms/century and the 2004 Indian Ocean earthquake is thought to have shortened it by 2.68 microseconds.[20] It is evident from the figure that the Earth has actually sped up since the initiation of the current system in 1971, and the rate of leap second insertions has therefore been decreasing.

    Though you are correct in asserting that leap seconds have only been added so far, there is no requirement for that and the current system has provisions for the removal of a "leap" second. In actuality, the overall trend has been for the length of an Earth day to shorten! [wikipedia.org]

    It's quite the rabbit hole, isn't it?

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  • (Score: 2) by JoeMerchant on Friday December 30 2016, @11:32PM

    by JoeMerchant (3937) on Friday December 30 2016, @11:32PM (#447648)

    I've seen a couple of things about the rotation rate of the Earth through history - human evolution was supposed to have happened mostly on a longer 25ish hour day, but then in deep history the Earth's rotation was supposed to have been much faster.

    I'm wondering if there's a net correlation between global temperature and rotational period - more heat, oceans expand, should be like the skater letting arms out in a spin to slow down - but then the glaciers melt and slide off their mountains into the ocean... probably a smaller effect than the expansion of the oceans, but a counterbalance of sorts. Put all of this against a backdrop of tidal friction, etc. I'm sure "scientists" and especially mathematicians can find all sorts of correlations (but, never prove causation...)

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    • (Score: 2) by AthanasiusKircher on Saturday December 31 2016, @01:10AM

      by AthanasiusKircher (5291) on Saturday December 31 2016, @01:10AM (#447700) Journal

      human evolution was supposed to have happened mostly on a longer 25ish hour day

      Huh? Based on what? Citation?

      (The only thing I could possibly think was connected to such a claim is the supposed sleep-cycle period in humans which years ago was measured to be slightly greater than 24 hours. But those earlier estimates as high as 25 or 26 hours have been revised with more recent research [harvard.edu], so the average circadian clock rhythm is now thought to be only a few minutes longer than 24 hours... and even that isn't exactly proof of a longer rotational period, since days are often a few minutes longer or shorter than the previous ones with seasonal variations.)

      • (Score: 2) by JoeMerchant on Saturday December 31 2016, @04:32AM

        by JoeMerchant (3937) on Saturday December 31 2016, @04:32AM (#447752)

        It may have been the sleep-cycle research. I'm remembering something from 25+ years ago, and lots of stuff from back then has been formally retracted, debunked, etc...

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  • (Score: 2) by AthanasiusKircher on Saturday December 31 2016, @01:02AM

    by AthanasiusKircher (5291) on Saturday December 31 2016, @01:02AM (#447697) Journal

    It's quite the rabbit hole, isn't it?

    It is indeed, but I personally can't understand why we feel the need to keep UTC aligned within 1 second to noon at solar zenith. The introduction of time zones already means most places happily live with a deviation of +/- ~30 minutes from that (and in many places more). DST introduces an additional hour offset that most people tend to complain about twice/year but otherwise never notice.

    Maybe once the error accumulates to 10 minutes or more in a few centuries, we can deal with a correction. But for now, people who need that 1-second precision (e.g., astronomers) already have UT1 [wikipedia.org] instead of UTC -- and for the professionals these days UTC isn't precise enough. And for those systems which don't need or want the corrections, they have TAI [wikipedia.org] and GPS time [wikipedia.org].

    We already have alternative time standards for EVERYONE who needs actual precision. UTC is just the average time standard for the common people. Who cares if it falls a few seconds or even several minutes away from aligning with solar zenith?

    • (Score: 2) by requerdanos on Saturday December 31 2016, @01:50AM

      by requerdanos (5997) Subscriber Badge on Saturday December 31 2016, @01:50AM (#447718) Journal

      Maybe once the error accumulates to 10 minutes or more in a few centuries, we can deal with a correction.

      Let me get this straight. You are proposing replacing the inconvenient leap second with the supposedly more workable ten leap minutes?

      Re:Simple solution is not so simple

      Mmm hmm.

      • (Score: 2) by AthanasiusKircher on Saturday December 31 2016, @06:43AM

        by AthanasiusKircher (5291) on Saturday December 31 2016, @06:43AM (#447781) Journal

        You are proposing replacing the inconvenient leap second with the supposedly more workable ten leap minutes?

        Actually, no. What I'm proposing is that we postpone this problem so far into the future that it's very unlikely anyone will give a darn about "mean solar time" by that point as a "universal" time standard. A few centuries in the future, we'll either all be run by AIs, have folks living on other planets so the idea of UTC would be rather meaningless, or whatever. Also, most people will likely adjust their schedules to the gradual drift of clocks over time, so nobody would even care to "correct" that 10 minutes, just as most people don't care about the DST shift a week or two after it happens.

        Even if we wanted for some bizarre reason to "fix" that problem in that far future -- by the time this ACTUALLY becomes a problem that the clocks are far enough off that anyone would give a damn, the earth's rotation will likely have slowed to the point that adding leap seconds is going to become a regular occurrence, so the current UTC system will ALREADY seem like an unworkable permanent solution. (It already IS an unworkable solution for the true long-term -- thousands of years -- due to the fact that we KNOW the earth's rotation will slow down, and at some point we WILL need more than an extra second per month.) Adding in 10 minutes or whatever by that point will be the LEAST of our problems.

        Also, we already have a time standard that tracks astronomical noon. It's called UT1. (Technically, the definition is a little more complicated than that, but there it is.) UTC is meant to be a pragmatic time standard that's precise enough for common, everyday people to use. Common everyday people don't care whether their clocks are off from solar zenith at Greenwich or whatever by a few seconds or a few minutes. Tinkering with the timeline on a variable basis every month (right now it has only happened in June or December, but theoretically could happen in other months) is a huge issue that will itself become obsolete too. Whether we continue the UTC plan for the next few centuries or not, we'll still have to face choices about changing implementation eventually.

        In the meantime, perhaps we can just dispense with a pain-in-the-ass half solution that is only convenient for observatories and very inconvenient for just about everyone else who designs a computer system which might be sensitive to arbitrary introduction of extra seconds. (Or removal of! Let's not forget that the current UTC standard allows skipping a second too! We haven't had the need yet, but given the variability in earth's speed, it could happen. How many systems will break when that wacko scenario happens, because nobody read the detailed timespecs and realized they might need to DELETE a second!)

        And maybe enough astronomers do benefit from having something that isn't quite as precise as UT1 but is as arbitrarily variable (but not more than a second) like UTC. That's great. Let them have their own time standard too. But why again are we ALL coupling our clocks to THAT standard for the 99.99% of computers and other systems that don't care when solar zenith occurs at Greenwich??

        • (Score: 0) by Anonymous Coward on Saturday December 31 2016, @08:34PM

          by Anonymous Coward on Saturday December 31 2016, @08:34PM (#447939)

          Leap seconds are a non problem for average people who do not operate to the precision of one second nor to the accuracy of one second per year. Only computers care and we have hacks to handle that situation. The first rule before taking action should be: don't make the situation worse!

          Anyone who truly cares about precision timekeeping already has a proper solution; the others don't care enough for a new system system em implemented.