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back to article Boffins quarrel over ridding world of leap seconds

The measurement and regulation of time could start to change this week if an ITU meeting in Geneva, Switzerland, gives the nod. International Telecommunication Union members are discussing whether Co-ordinated Universal Time (UTC) should be set using a system that does not factor in the Earth's imperfect spin – which …

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Unix time

Seems pretty clear you should never adjust unix time, but rather adjust the time zone data used to turn it into yyy-mm-dd hh:mm:ss.

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Time

Unix StarDate 57429.29....

That is all....

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Stop

... servers, air traffic control, GPS and space missions...

This sounds too Y2K for me.

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Anonymous Coward

You'll enjoy 2038 then.

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Go

I use 64 bit unix...

So 2038... not a problem,

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2038

""You'll enjoy 2038 then.""

You are confusing method with implementation. The Unix problem can (will) be solved by moving to 64 bit integers.

(At Tue Jan 19 03:14:07 2038 GMT Unix time as a 32 bit number wraps round)

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FAIL

Yeah, so?

I can handle 64-bit integers on my extremely-8-bit Acorn BBC.

The problem is in the stored size in all the applications, and not only on your own system, that use the Unix time format. If those aren't changed from 32 to 64 bits, you're still fucked.

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Just to be accurate. This is where time is expressed using a 32 bit signed integer representing the number of seconds since Jan 1st 1970.

I note that the OS I use (vxWorks) now declares this as an unsigned integer, thereby putting off the evil day until 2106

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Anonymous Coward

What happens if you want to store a date before 1970?

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not Y2K

The issue is what happens if the leap second adjustment is made during some critical operation and whether different equipment remains synchronised during the time update. Space missions typically pick some fixed time datum (e.g. launch) and measure time relative to that datum, so such adjustments are largely irrelevant.

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computers can easily cope with leap seconds

Oh really?

But the devil is in the detail. Many Unix machines used to have their hardware clocks set by counting the elapsed seconds since, i think, 1st Jan 1970! Then the software clocks were synced by atomic clocks using NTP or the likes. I'm not sure that this still holds but nevertheless

this is important because time must be tracked even when the kernel is not running.

Not sure that i agree that they can easily cope with leap seconds. That has to be only a maybe.

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Anonymous Coward

$ man localtime

[snip]

tm_sec The number of seconds after the minute, normally in the range

0 to 59, but can be up to 60 to allow for leap seconds.

[snip]

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One Question

So if we go with the atomic time & ignore sunrise, does this mean that at some point we'll end up with '12 midnight' some time in the middle of the afternoon? Or maybe starting work at '9am' - two hours after sunset.

IMO, despite the difficulties behind a computer fix, fixing people's perception that 9am should be in 'the morning' and midnight should be 'at night' is going to be much much harder.

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Yes, but even if you are losing 1second per year it's going to take 12 * 60 * 60 = 43,000 years to accumulate 12hours of difference.

I think the proposal is to have a leap hour every few millennia to handle this.

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WTF?

It all depends

how fast the earth's rotation slows down, no?

I am more worried that gravity will drag us down into the dust as the centrifical force generated by the earth's spin is reduced.

<sigh> We all end up there anyway.

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Unhappy

If this is what is worrying you then you really should not go and stand at either the north or the south pole.

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@Alain Moran

The time under discussion here is UTC (or GMT) rather than local time. Considering that where I live (Australia), the sun generally rises somewhere between 7:30 PM and 9:00 PM UTC, for the majority of the planet UTC doesn't correspond to sunrise/sunset anyway.

So having UTC refer to a fixed number of seconds rather than the wobbly rock we're sitting on does make sense. Although calculating local time might become a bit more fiddly than just adding or subtracting X hours from UTC, the difference would be small enough for the next few thousand years that for most practical purposes it would be insignificant.

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Headmaster

Centrifugal force

There is no centrifugal force - it's inertia (Newton's laws of motion). Gravity acts as the centripetal force.

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"It's inertia"

I'm cool with inertia. Thanks for the heads up

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Angel

No centrifugal force?

A laughable claim, Mister Bond, perpetuated by overzealous teachers of science. Simply construct Newton's laws into a rotating system and you will see a centrifugal force term appear as plain as day.

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Anonymous Coward

<xkcd>

come now, do you really expect me to do coordinate substitution in my head while strapped to a centrifuge?

</xkcd>

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Yep.

Thats why people in equatorial countries are shorter y'know.

Go tell-em.

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FAIL

@Local Group

Your secondary school physics teacher is rolling {his eyes|in his grave}.

Additionally, the Grammar Gestapo wishes to point out that it's _centrifugal_,

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Unhappy

Leap-hou every few millennia

Yeah but that relies on people REMEMBERING: will they leave a note, or an obelisk, or something??

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@ Stoneshop

My physics teacher rolled his eyes at me plenty when he was still spry. All my teachers did.

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Headmaster

Crushed...

If the Earth stopped rotating completely, you would be mercilessly crushed under the devastating impact of a whole 0.03ms-2 of additional effective gravitational force...

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Mushroom

Inevitable, really

Consider this: In the past, noon was defined as when the sun was at its zenith. That failed when we started having transportation fast enough, and clocks accurate enough, to allow detecting that noon here wasn't noon there.

So then we moved to time zones, and accepted that noon didn't always mean "highest sun".

Now, between electric light and world-wide communications, time being tied to the fact we live on a round ball is getting unwieldly - my co-workers in the UK and I have to deal with a six hour difference on a daily basis, and one of my co-workers in California just gets up 2 hours early to avoid the issue.

So what if TAI is minutes or more off what the earth is doing? Very few people live where noon in their time zone is solar zenith, so we are already dealing with this. Just get over it.

(/me pulls pin...) And let's just skip Daylight Savings - pick a time offset and stay with it (/me throws....)

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Daylight savings was invented by people who thought you could take time off the start of the day, tag it on the end and have a longer day. IT IS AN ABOMINATION UNTO NUGGAN.

However leap seconds and suchlike are a necessary evil, otherwise you end up with calendar year slowly drifting through the siderial year. Not adding a leap second will very, very, very slowly cauyse havoc with calendars and lead to some future generation having to reset the calendar to make it match the siderial year again, as with the Gregorian to Julian calendars. Our descendants in the year 28822 will rue the day we stopped adding leap seconds.

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Unhappy

Re: Daylight savings

I pray those Kentish folk who want us to permanently pretend it's an hour or two later than it is never get their way. How the hell will I feel like getting out of bed on a winter morning if it doesn't get light until half past nine?

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Human race still exists in 26,000 years?

I like your optimism.

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Slowing Down

I would much prefer going back to what we had before leap seconds: having a second of civil time which corresponds to the Earth's rotation, even though it is slightly longer than the SI second. This avoids the potential for software problems.

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@John Savard: How long since XXX?

The trouble your proposal is that it makes it very difficult to accurately work out the time between two dates. The answer would necessarily be very ambiguous! For example the answer to the question 'how many seconds were there in 2011?' would depend on whether you're taking the current length of a second as the basis, or the length of a second at the very end of 2011, or the mean second length during 2011, and so on.

The REAL answer to the problem is to get the operating system boys to sort out time properly. Pretty much every OS, programming library and application out there has always completely ignored leap seconds purely because the original programmers were too lazy to find out what UTC actually is, which is crazy considering UTC was defined decades ago back in the early days of computing.

The only people who have actually got it right so far as I know is the astronomers; not surprising as they do actually care about accurate time differences over long periods of time. The IAU's SOFA source code library has all the routines needed to accurately convert between UTC, TAI, etc, taking proper account of leap seconds.

The only disadvantage of SOFA is that it needs a static table of leap second data manually updated (and your code recompiled) every time there is a new leap second (they're not predictable in advance). It uses this table of all the leap seconds there have ever been when converting between TAI and UTC. In this day and age it should be trivial for something like NTP to communicate that table to OSes automatically. It would take some work to update apps to use something like SOFA instead of the inaccurate libraries that are used in the mainstream today, but it would completely solve the problem for ever.

Changing OSes and software is probably a whole lot easier to do that than it would be to change all the laws, working practise, train timetables, etc. etc. when humanity finally gets fed up with 0900 being increasingly early in the sidereal day. My great great....great grandchildren don't want to be contractually bound to turn up to work at 0900 if that's in the middle of the night.

I reckon that this is something that Linus Torvalds could single handedly solve. He can change the Linux kernel and has enough influence over NTP and glibC to make it happen. If Linux gets it right, every one else might follow.

Getting it right in the OSes would make a tremendous difference to software programmers who have to worry about time. For example, how many times have Apple failed to get their iPhone OS alarm clock to actually work as an alarm clock? How many people with electronic calendars have been frustrated by the inability to properly deal with daylight savings and time zones?

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Trouble is then you don't know in advance how long a second is going to be - the rotation is constantly changing - Which makes timing stuff a little bit tricky

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re: Slowing Down

Varying the length of a second doesn't really work, as it's not that it's currently wrong, but more that it's getting more and more wrong as the earth slows down - a variable second dependent on the Earth's rotation doesn't really work.

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All very interesting

But a second is a second is a second and needs to stay that way. Variable length seconds are a nonsense concept. What is the world record for the 100 metre sprint?

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@bazza: An emminently logical proposal sir,

are you certain you should be posting here?

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@It wasnt me: re: a second is a second

Spoken like someone who is completely unfamiliar with the differences between sidereal, solar, and atomic time; the origins of time keeping; the development of naval navigation; or even the importance of knowing when to plant the crops, which really, is pretty basic and critically important when you get right down to it.

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Well the current system has to deal with the odd 'quarter of a day' error. So why not do 'gregorian calendar with this year's fudge factor' and add that factor to seconds.

1 atomic second = 1 atomic second + (or minus) 0.0000000072, or whatever.

That takes care of all the inconvenient dicking around and would be smoother for all concerned. As a rider to this policy, I would suggest that a law compelling every single farmer to own a fucking torch (with a public emergency fund for really skint farmers) and we can stop all this summertime/wintertime crap.

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>own a torch

Its not just farmers is it. Its all the outdoor trades, builders and the like. And what's going to happen to the accident rate and the traffic flow if white van man is on the road for 9 and 5 like the rest of you, instead of 8 to 4?

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DST doesn't affect farmers in the slightest anyway, they all get up at godawful in the morning and go to bed and fuckmeit'sdark in the evening no matter what the clock says. DOn't blame the farmers, blame the politicians who wanted to have a long afternoon in the stranger's bar.

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Rubbish!

This argument is rubbish. I'm an ex-pat living in Sweden and where I live in the winter, at it's worst, the sun doesn't rise until 09:30 and then sets at 14:30. Builders don't stop work here just because it's winter and it's dark (they're building a new 18 storey appartment block across from where I work and they've been working all winter), and there are no significant increases in traffic accidents just because it's dark (there are more due to the onset of winter weather but not because of the dark). As I said this argument is rubbish.

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Only a mediocre rant, Mr Brammer,

the repetition is good, but you need to work harder on multiple capital letters and maybe add some excess punctuation. But good marks for completely missing the key point: I was relating accident rate to increased traffic density, not hours of darkness. I'm quite sure you're right that the Swedish outdoor trades adapt well to winter darkness, but I'm less sure that its a useful comparison to southern English ones.

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'A Method For Deterministic Time Synchronisation And Co-Ordination In Fixed And Moving Reference Frames For Portable Electronic Devices With Or Without Roundy Corner Bits'

I think the ITU are knackered whatever they do. I imagine Apple have already patented something like the above though the *cough* USPTO.

What I'd like to see is a good shake up of the entire calendar, starting with putting New Years Day where it (roughly) should be... December 21st.

@moiety: There's already such a fund. It's called the Common Agricultural Policy. France knick loads of it. It keeps those inefficient, not-so hardworking rural French farmers, well, not very busy but quids in ;)

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Anonymous Coward

where it should be?

I think New Year used to start at the beginning of Spring or the Vernal Equinox, as new growth for the New Year started. January and February were added as sort of "leap months".

As for twice per year juggling with the clock or moving UK to GMT + 2 or whatever, why? Start times for work and school are pure conventions. In Switzerland, work tends to start at around 0800, lunch tends to be at about 1200. As somebody wrote, farmers are ruled by real time as indicated by the sun. Just start the school/working day at the naturally appropriate time for the season.

I never can understand why travelling to work in the dark, when one is tired and rushing, should be any safer than going home in the dark, when presumably most people are awake as they have no intention of going to sleep as soon as they get home. At school in England, in the days when we had daily sport, in Winter we simply adjusted our timetable to have sport in the afternoon and lessons began at about 16.30 i.e. we made use of the daylight without adjusting the clocks. Surely, that is the proper way if we are not mindless machines.

Sad that anyone wants our clocks regulated by some means that is unrelated to the rhythm of the physical world in which we live. As it was, UK did not adjust from an artificial to an almost natural calendar until 1752, by which time the adjustment of the eleven days disparity caused a lot of upset, even riots. Now we want to return to a dislocated, artificial (if perfect) system that will need a more awkward adjustment at some unspecified time in some very roughly specified future and society.

Time measurement is just a tool. Tools should fit the normal user in his normal environment, not the other way around.

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@AC 11.26

To clarify: where it should be - to me. I wasn't actually trying to draw a reference to bygone days.

IMO the most 'logical' day for New Year's day is when the sun is at (or one day past) it's lowest altitude above the horizon and definately not when the sun is at one of the equinoctial points... But then I also see sidereal as more intuitive and natural than say, solar :)

"Time measurement is just a tool. Tools should fit the normal user in his normal environment, not the other way around."

Ah'ha. HCT? Human Circadian Time. That may put me at odds with the bloke next door who is on permanent nights. He's on HCT +12. (I jest of course).

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Choices for the start of the calendar did depend on solar time,

but whether it was equinox or solstice seems to depend on the culture. Early months also tended to be exactly 30 days, but this led to other obvious problems. We will always have to deal with occasionally straightening out a mess because sidereal /= solar /= atomic, and each has its legitimate use and purpose. Although it does seem to me that for most practical purposes these days we would be better off holding on the leap seconds until there is a leap minute and then making one large shift that everyone is actually prepared for rather than more frequent shifts for which we are unprepared and which are prone to truly bollux up things.

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Someting very ironic here...

A lot of the history of time measurement, especially dates, was developed because of all the problems caused by calendars that didn't synch with terrestrial rotation. Now it's proposed to reverse this!

If, by the year 37whatsit, our time synch systems are not dealing with time far far better than they do now, I think our descendants will need shooting.Still, maybe by then we'll be off this planet, and terran time will be irrelevant. Stardate anyone? But sufficient to the day and all that.

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Unusual arguments?

Whilst I totally respect his academic credentials, I'm not sure that "abandoning leap seconds would break sundials" or claiming ">5000 years of human practice" - neither of which could claim any degree of accuracy beyond +/- several minutes, at least for most of the 5000 years - are the strongest points he could have made ...

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@AdamT: You're missing the point

So long as humans want to go to sleep sometime after dark and wake up sometime around about when the sun comes up, we will need a time scale that is aligned with the sun.

We either stop caring about 0800-ish being the time we wake up and go to work, or we arrange matters so that 0800-ish is when the sun comes up. Trying to coordinate the former across the world without causing a lot of havoc is going to be difficult, because actually there is so much in our lives that is based on clock time being equal to sidereal time.

If the ITU does abandon leap seconds the whole world would occasionally have to re-align every time dependent aspect of our lives (timetables, contracts, laws, telephone systems, etc. etc) to keep it in track with the fact that humans live sidereal lives. Changing all that in one go and getting it right sounds a lot harder than dealing with a leap second every now and then.

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