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.
Related Stories
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
(Score: 0) by Anonymous Coward on Friday December 30 2016, @05:37PM
Give all computers a break for 1 second out of the year. Outside of cruise missiles, landing planes, and autonomous cars there are not a whole lost of devices that care about the time+date that it should affect, and most that it COULD should be handled by a time protocol or adjustment during standard maintenance times, of which any serious industrial equipment will have at least one per year.
(Score: 4, Informative) by martyb on Friday December 30 2016, @06:23PM
It seems easy, but the reality is far more complicated. For some background, please read Wikipedia's entry on the Leap Second [wikipedia.org]. Pay special attention to the section examples of problems associated with the leap second [wikipedia.org]. If it really were that easy, I'd suspect that some of the people who are actually responsible for the calculation and distribution of notices about leap seconds would have found that easier way by now.
There have been proposals to abolish the leap second [wikipedia.org] and none have been ratified because of issues with it.
The best proposals I have seen are analogous to how *nix systems have the system clock set to UTC and then compute/display time based on an offset from that. Wikipedia concisely states this as follows:
This is not without its own problems, as there is the question of what do you do with all of the existing devices that are already out in the field.
See, also, the section Workarounds for leap second problems [wikipedia.org] for some other ideas and complications.
Wit is intellect, dancing.
(Score: 2) by JoeMerchant on Friday December 30 2016, @06:48PM
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.
Think of all the fun that process engineers and others will have with a variable second that changes by 0.00001% every 10 years. Other than GPS clocks and similar truly time-critical devices, the change would be deep inside the normal process variations.
🌻🌻 [google.com]
(Score: 2) by martyb on Friday December 30 2016, @07:06PM
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]:
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?
Wit is intellect, dancing.
(Score: 2) by JoeMerchant on Friday December 30 2016, @11:32PM
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...)
🌻🌻 [google.com]
(Score: 2) by AthanasiusKircher on Saturday December 31 2016, @01:10AM
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
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...
🌻🌻 [google.com]
(Score: 2) by AthanasiusKircher on Saturday December 31 2016, @01:02AM
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
Let me get this straight. You are proposing replacing the inconvenient leap second with the supposedly more workable ten leap minutes?
Mmm hmm.
(Score: 2) by AthanasiusKircher on Saturday December 31 2016, @06:43AM
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
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.
(Score: 2) by sjames on Friday December 30 2016, @08:34PM
The vast majority of systems really don't care that much. That's why the news isn't flooded with reports of people stuck in elevators or losing power of having their DVRs freak out every leap second.
Other cases REALLY do care, but even most of them will be OK if they are set to the same master clock.
One problem is that the 'official' handling of a leap second ins't even something most computers are equipped to do (nor analog clocks for that matter). Officially, a leap second is handled by having the clock count (in UTC) 23:59:59 -> 23:59:60 -> 00:00:00. But practically no computers can even express 23:59:60 as anything but a denormalized alias for 00:00:00 since they keep time internally as the number of seconds since the epoch. Same for an analog clock.
More feasible (but not quite per standard) would be to subtract one second from the system clock just as it would otherwise tick over to 00:00:00. This is what the official NTP servers do. It's at least within the design of the system to be able to express that, but it can still be a big problem if you want to know how many times an event happened in the second of 23:59:59 compared to 23:59:58 since the former would effectively last 2 seconds, making it look like a huge spike in the rate.
In practice for most systems that care enough to synchronize with NTP, they simply run as usual and suddenly at 00:00:00 they find themselves 1 second ahead and slow the tick of their clock slightly so that they fall back in sync with NTP over the next few minutes (known as slewing the clock). In most cases, as long as the slew rate is the same throughout the consistent time domain and everybody syncs to the same clock, this is the right thing even if it is far from the official standard. It introduces a small and generally tolerable error for a few minutes. A number of unofficial tier 2 and above (in NTP, higher tiers are further removed from the atomic clock) do more of less this themselves.
Google deliberately slews the second starting hours before the leap second and ending hours after. IMHO, it's a lot of effort for a small gain, but as long as everyone in a consistent time domain uses the google servers, it's fine though some object to creating yet another time standard.
As you point out, for equipment that can have a downtime for maintenance and care more about consistent time than absolute correctness such as aircraft navigation, just do it during the next scheduled maintenance.
Just to add to the confusion, a consistent time domain is only consistent to within a margin of error.
(Score: 2) by krishnoid on Friday December 30 2016, @10:11PM
Google deliberately slews the second starting hours before the leap second and ending hours after.
Silly question -- contextually, it doesn't seem like the dictionary definition of 'slew' describes this sort of adjustment. Has this definition changed ('slewed' :-) somewhat, and can someone provide a reference for it here?
(Score: 3, Informative) by sjames on Saturday December 31 2016, @12:10AM
For bnetter or worse, it's the word chosen for use in various documents on clock handling in a computer. It is used as opposed to stepping where the clock is simply set to the corrected time instantly. Slewing also guarantees monotonic time (it never goes backwards).
Google "ntp clock slew" for a bazillion references.
(Score: 2) by mmcmonster on Friday December 30 2016, @05:48PM
Couldn't they pick any other day of the year to add the second? Why do it on the one day where people are focused on an exact second variation in time?
Or do they want to be the focus of conversation amongst non-geeks?
(Score: 5, Informative) by Dunbal on Friday December 30 2016, @05:53PM
It is one second in the day, not one second in every single time zone in the day. Unless your New Year happens to coincide with the UTC time zone, the leap second will have come and gone and you'll be none the wiser.
(Score: 2) by Gaaark on Friday December 30 2016, @06:11PM
Ah, i see you've played knifey--leap second before!
--- Please remind me if I haven't been civil to you: I'm channeling MDC. ---Gaaark 2.0 ---
(Score: 3, Funny) by maxwell demon on Friday December 30 2016, @07:06PM
As it does in the UK. Obviously it's a revenge for the Brexit. ;-)
The Tao of math: The numbers you can count are not the real numbers.
(Score: 2) by Dunbal on Friday December 30 2016, @09:46PM
Get to stay a whole extra second in the EU huh? Don't worry, Theresa May and co are in absolutely no hurry to Brexit, apparently. Looks like it's probably going to be passed along to the next generation of politicians, and the next, and the next. See they figure it was mostly the over 40's that voted for Brexit. All they have to do is wait and we die off.
(Score: 2) by hendrikboom on Friday December 30 2016, @09:33PM
I get my leap second squeezed in just before 7PM.
(Score: 3, Funny) by Gaaark on Friday December 30 2016, @06:29PM
it just means Trump won't be president for ONE. MORE. SECOND!
--- Please remind me if I haven't been civil to you: I'm channeling MDC. ---Gaaark 2.0 ---
(Score: 0) by Anonymous Coward on Friday December 30 2016, @06:43PM
I just spent that long reading your post...and now, I'm in the hole.
I propose a leap year, an extra year that's inserted without changing the date. After a New Year's Eve that lasts 365 days (and one second) we'll all be ready for the Trump era.
(Score: 2) by maxwell demon on Friday December 30 2016, @07:07PM
And give your employer an excuse to not pay you for a whole 365 days?
The Tao of math: The numbers you can count are not the real numbers.
(Score: 0) by Anonymous Coward on Saturday December 31 2016, @02:47PM
Another year of 2016! Haven't enough celebrities died already? ;)
(Score: 2) by PinkyGigglebrain on Friday December 30 2016, @05:58PM
2016 hasn't already been around long enough :(
I honestly can't remember any other year that I wanted to be over as much as this one.
"Beware those who would deny you Knowledge, For in their hearts they dream themselves your Master."
(Score: 0, Redundant) by Anonymous Coward on Friday December 30 2016, @06:09PM
why?
please stop associating time stamps to unrelated things.
feel free to call 2016 "the year of the quick fox who jumps over the lazy dog", if that will make you feel better.
for instance:
"please let the 21st of december be over faster, I don't like it when the sun is hidden for 18 hours of the day" would make sense.
"please let the 21st of december be over faster, I don't like it because a meteor struck the planet this morning" makes absolutely no sense.
when you complain about people dying or votes going against your personal desires, and relating it to the year you're in, you are definitely in the second scenario.
(Score: 1, Touché) by Anonymous Coward on Friday December 30 2016, @06:49PM
Ah you can't wait for Trump to become president either. Check!
... or is it that old celebrities died, like they do every year.
(Score: 3, Insightful) by martyb on Friday December 30 2016, @07:30PM
Or that, inescapably, I'm made ever-more aware of my own mortality?
If these ageless memories of my youth are now meeting their [un]timely demise, then maybe my life's youth has passed, and my remaining days draw nearer to their end. Very few indeed are they who, in full health and well-being, easily envisage their own passing.
Wit is intellect, dancing.
(Score: 2) by butthurt on Sunday January 01 2017, @11:01PM
Not all were what I'd call old. Prince died at age 57, George Michael at 53, and José Fernández at 24.
https://en.wikipedia.org/wiki/Prince_%28musician%29 [wikipedia.org]
https://en.wikipedia.org/wiki/George_Michael [wikipedia.org]
https://en.wikipedia.org/wiki/Jos%C3%A9_Fern%C3%A1ndez_%28pitcher%29 [wikipedia.org]
(Score: 0, Offtopic) by Ethanol-fueled on Friday December 30 2016, @09:06PM
This was a truly shit year, so go ahead and mod me offtopic* because I'm going to participate in this little circle-jerk.
On the public level, we lost all those great musicians (as well as came to the realization that there will be nobody even close to those people, ever, given today's shit music written mostly as lullabies for antidepressive medication-addled kids to be piped into stores to make them buy more shit).
We had a particularly vicious election season, which really brought out the most ugliness in America since the civil-rights era. Those who didn't see before finally did see that mass-media are paid actors rather than respectable journalists. That Democrats really are the same as neocons. That Americans really are stupid enough to be divided over increasingly petty issues by design rather than work together for common interests.
Our first "Black" president was the biggest disaster for race-relations since Ronald Reagan declared ketchup a "vegetable" to feed what he called "welfare queens." The man who will supersede him as President is significantly divisive -- although, in a good way, because somebody had to muster the balls to kick out the goddamn Latin Leeches and Durka-Durka scum Baraq Hussein Soetoro is pozzing our country with. He lost, so like a petulant crybaby he's implementing scorched-Earth tactics on his own country. I predict he'll have a seat at the UN pretty soon, like David Cameron will.
On a personal level, it was pretty shit. One bad setback after another, and a pretty shitty way to remember graduating from college. Like many people, I can't admit to my own family that I voted Trump without significant backlash - I did to one of them as a litmus test, and all I heard were the usual MSNBC talking points - "He's a RAPIST!" I'm just glad this year's fucking over.
* Note: only shit-eating cocksuckers mod me offtopic
(Score: 0) by Anonymous Coward on Friday December 30 2016, @08:19PM
Parent is correct. If precision down to the second at all times is required, you don't use UTC. You use a time system without leap seconds, at the least. If you notice, many times legal documents will specify that a policy or contract will begin at some date at 12:01 AM
to eliminate the ambiguity of when a new day begins: at midnight, or the second after? (For the record, the widely accepted answer is one second after 12:59:59 PM, i.e., the day starts at midnight.)
I would go so far as to say if you are using UTC (rather than Unix, GPS, or TAI time), you shouldn't expect resolution of more than a minute.
(Score: 2) by darkfeline on Friday December 30 2016, @08:45PM
>If precision down to the second at all times is required, you don't use UTC.
UTC is precise. What isn't precise is UNIX time; note the difference. Every single moment in time corresponds to a single point in UTC. UNIX time is defined in terms of UTC, IGNORING LEAP SECONDS. The problem here is that UNIX time will skip, but UTC won't.
If we wanted to solve this problem, we would make UNIX time v2, which could be based off of TAI, or UTC including leap seconds. I'm not sure the transition costs would be worth it though.
> If you notice, many times legal documents will specify that a policy or contract will begin at some date at 12:01 AM
to eliminate the ambiguity of when a new day begins: at midnight, or the second after? (For the record, the widely accepted answer is one second after 12:59:59 PM, i.e., the day starts at midnight.)
That's only a problem because normal people use one-based indexing, which is not mathematically sound for continuous scales (you end up with a "hole"), whereas zero-based indexing is mathematically sound.
Note the distinction between discrete scales, which would be used when counting, and continuous scales, which is a superset of discrete scales.
Join the SDF Public Access UNIX System today!
(Score: 0) by Anonymous Coward on Saturday December 31 2016, @02:08AM
You are confused.
Unix time is defined as seconds elapsed since Jan 1, 1970 without including any leap seconds. We agree on that. That doesn't make Unix time any less precise than UTC. All UTC does with its leap seconds is to make the calendar year longer; specifically, it makes the month (even more specifically, the particular minute within the month containing the leap second) one second longer than usual, i.e., instead of that particular minute containing 60 seconds, it contains 61 seconds. That's all. There are no "gaps" in Unix time just as there are no "gaps" in TAI or GPS time. Unix time is just a running count of seconds elapsed from a starting point just like TAI or GPS. One can convert UTC -to- (Unix time, TAI, or GPS) with zero loss of precision -or- the reverse just by applying a historical table of when leap seconds were applied.
(Score: 0) by Anonymous Coward on Saturday December 31 2016, @04:54AM
The way Unix time kludges in "support" for leap seconds (it doesn't support them, it employs hacks to sync back up with UTC) is pretty ugly and is explained in detail here:
https://en.m.wikipedia.org/wiki/Unix_time [wikipedia.org]
(Score: 2) by maxwell demon on Saturday December 31 2016, @12:23PM
The whole point of the original definition (seconds since a certain point in time) was perfect. The leap seconds could (and should) have been considered during conversion from/to local time, just as the time zone is. As bonus, you'd get correct handling of the leap second automatically as soon as the relevant tzdata is installed, even if at the time of the leap second no external time source is available.
The Tao of math: The numbers you can count are not the real numbers.
(Score: 0) by Anonymous Coward on Saturday December 31 2016, @04:16PM
I agree completely. That would be the obvious, straightforward, and unambiguous way to solve it, i.e., the correct way.
Therefore, that way never stood a chance. Computer nerds LOVE the complicated, undependable hack more than anything else. Why fix it when you can kludge it instead? I think it's because the people who came up with the hack thought backward compatibility with crappy time libraries would make times be off by some seconds potentially, but their leap second "hack" pretty much GUARANTEES that will be the case forever going forward. It takes a very clever mind to come up with a solution this stupid.
(Score: 1, Informative) by Anonymous Coward on Friday December 30 2016, @10:39PM
I'm guessing you meant 11:59:59 PM, not 12:59:59 PM.
(Score: 0) by Anonymous Coward on Saturday December 31 2016, @01:36AM
You caught my typo: I meant 11:59:59 PM
(Score: 0) by Anonymous Coward on Saturday December 31 2016, @06:55PM
Have A Nice Day.