The Future of Leap Seconds

@10u8 writes "Since 1972 precision clocks around the world have ticked using atomic seconds, but earth rotation is slowing down. Leap seconds have been inserted in order to keep noon happening at noon, but they upset some timekeepers. Recent discussions have considered discontinuing leap seconds in UTC, and a colloquium in Torino next month will present results. It is a matter of international significance."

Comments

Why?

[k-0s]

I can't see why they hate leap second. I'll be damned if I am going to eat lunch at what is called 8:00 in the morning because they don't want to keep leap second. Grow up, we have leap years and human time keeping is not an exact science as the Earth tends to spin the way IT wants not the way we want.

Re:Why?

[Jason1729]

The problem with leap days has nothing to do with the Roman calendar. It is because the time it takes the Earth to revolve around the Sun is not an integer multiple of the time it takes the Earth to rotate on its axis. The Lunar calendars you mention have leap-months.

Jason
ProfQuotes

Re:Why?

[Waffle Iron]

I don't think that is accurate. the concept of leap years is because the roman calendar sucks.

The concept of leap years is because the ratio of the length of a year divided by the length of an earth day is not an iteger. No calendar can get around that fact. You either add intercalation days whenever the remainders of your divisions exceed 1, or you keep track of huge numbers and cycles that greatly complicate your timekeeping.

The Julian roman calendar did suck because they didn't get the ratios quite right and it drifted. (The Gregorian calendar fixed this for all practical purposes.) However, prior to Julius Caesar, it sucked even more because there was no mathematical formula. Instead, priests were supposed to observe the sun each year and decide when leap days were needed.

The priests were also involved in politics, so they chose to shorten political terms more often than not by omitting leap days. IIRC, by the time the Julian calendar was instituted, the Romans were off by several months due to these partisan shenanigans.

Re:Why?

[aztektum]

I don't get why being that anal about time keeping is so important anyway. I guess with all the high dollar electronic transactions that go on these days there and what not, but for the average chump going about day to day... if the sun is in the sky it's day time, if it's not, it's night. If it looks like it's in the middle of the sky it's time for lunch.

What's the big deal? Can someone enlighten me?

Re:Why?

[foog]

time "ticks" at a constant rate in any particular reference frame (SR), which is how time standards are defined, anyway.

Satellite clocks have to be relativistically corrected, especially for applications like GPS.

Re:Why?

[Bob Fr]

There is time as used by humans vs other measures. Its purpose was to define the time that the trains ran on and is very convenient and has only passing relationshipt to the position of the sun -- those at the edges of timezones can be off by an hour or two or more.

Leap seconds are a fine correction for gear that, unlike humans, cares about nanosecond accuracy.

The serious problem with leapseconds is that they make minutes context sensitive and essentially all computer software presumes seconds are not context sensitive.

The simple fix is to keep leap seconds as a correction factor but not confuse it with the time that humans and their computers use for normal use.

The leap second is the kind of bug that appears when you have experts who know too much and are totally clueless about any usage other than what the care about.

It was simply a stupid mistake to foist it on humans and there. They should apologize and simply keep their mitts of social mechanisms like the clock.

Re:Why?

[Anonymous Coward]

Because time is crucial to all sorts of physical and scientific endeavors, such as planetary motion, navigation, GPS, etc. We need an accurate standard, or stuff quits working.

Re:Why?

[Okonomiyaki]

Interesting. So is there any way that we can use a similar technique to get Nov 2004 to arrive a little sooner? Please?

Re:Why?

[pVoid]

It's quite simple why:

Imagine this simple, granted exagerated, scenario: You park your car somewhere on June 5th 2003, someone comes and says there's a special leap day on June 6th, and it becomes June 7th...

All of a sudden your car seems like it's been there for two days on paper.

Imagine how difficult it will become to measure elapsed time (just strictly from a computational POV) if we start adding and removing seconds here and there.

This problem is a huge one.

In fact, the earth is slowing down to the point that:

The slowing rotation of the Earth results in a longer day as well as a longer month. Once the length of a day equals the length of a month, the tidal friction mechanism would cease[...] That's been projected to happen once the day and month both equal about 47 (current) days, billions of years in the future. If the Earth and Moon still exist, the distance will have increased to about 135% of its current value.... from link.

So what's the principle we abide by? Our measurement of a day, or hour stretches? or we change what time we wake up at? What happens if we colonize Mars?

It's a crucial problem that requires lots of foresight.

Re:Why?

[SpaceLifeForm]

IIRC, all leap seconds when inserted or deleted, is well planned in advance. IIRC, GPS is prepared for these events also. Here's a link.

Re:Why?

[Guppy06]

One word: Longitude. Generally speaking, you determine your longitude by comparing what the local solar time is (determined by looking at the position of the sun in the sky) and comparing it to the time in some reference point (say, the Prime Meridian). Every hour's difference is 15 degrees of longitude.

Obviously, there have been all sorts of tweaks and modifications to this formula in the past 200+ years or so, but the basics are the same: You need to know what time it is to know where you are. Your precious little GPS receivers wouldn't work if they could get as accurate a time measurement as possible from the US Naval Observatory.

(Some historians have suggested that the US won the war in the Pacific because US ships had more accurate clocks.)

Re:Why?

[gschwim]

...because he's been so successful creating jobs/boosting the economy in the past...

Yes, Bush simply hasn't gotten around to saying "Let the economy be prosperous again," which is the real problem. (Yes, that *is* sarcasm, in case you were wondering.) Or are you saying something different?

Seriously, the economy was on the downturn WAY before he took office. It's somewhat like driving a supertanker if you will -- it takes a good deal of time just to turn 90 degrees from your original course. Economies are well know for lagging the geopolitical times by a significant margin, and changing their trends is not something that can be done in a single month or even a single year. The true economic effects of the present leaders of our country may likely not be fully realized until *after* they've taken leave of office.

The prosperity of the 90's was due largely in part to the policies of the presidents that preceded Clinton. He had little (if anything) to do with it. After all, he was too busy with "other" things.

Re:Why?

[daeley]

First of all, whether or not an observer can tell how many matches are in a matchbox is immaterial--nay, completely unrelated to the fact that there is a particular number of matches in the box, a precise number that can be determined.

Secondly, time needs not be exact for most people most of the time, but perhaps you can recognize that there are certain applications, especially scientific and technological, for which a measure of exactitude is quite necessary.

Thirdly, I would venture to say that the society depicted in 1984 would rather that people be unable to tell what time it was.

Lastly, all these fitful worries are meaningless, because my man Flavor Flav always knows what time it is. Word.

Re:Why?

[Slack3r78]

This has to be the most tired, rediculous argument I continue to hear on a regular basis. No, the results of economic policy don't occur overnight. However, in the 12 years covered by the Reagan and senior Bush administrations, there was a general economic lull and by time Bush left office in 1992, the federal debt was over FOUR TIMES what it was when Reagan entered office in 1980. While government spending does encourage private spending, letting the federal government bleed cash profuciously IS foolish in the long run.

When Bush entered office in Jan 2001, the federal government was running a $127 billion surplus. The projected figure for the 2003 fiscal year is a $300+ billion DEFICIT. Simply put, the federal government will lose more money this year than it payed back off under the 4 years of surplus combined. How is this wise economic policy? The downturn may have started before Bush, but he hasn't done anything of significance to reverse it. And of course, Clinton had absolutely nothing to do whatsoever with the economic prosperity of the mid 90's. All those silly trade deals and the callaborative work he did with other nations most certainly did nothing to help at all. International agreements, who needs'em?

Re:Why?

[renard]

Your precious little GPS receivers wouldn't work if they could [not] get as accurate a time measurement as possible from the US Naval Observatory.

Not true. GPS receivers get all the information they need directly from the GPS satellites - which track their own "GPS Time" that dispenses with the leap-seconds.

You're right that having an accurate astronomically-relevant time is important for navigation - if you are determining your position with a sextant. It's the decreasing relevance of sextants to the world of navigation, and the increasing need to keep electronic equipment of all sorts in lock-step, that is driving this movement away from the leap-seconds.

See a summary of the issues from one of the US Naval Observatory scientists in charge of this stuff: PDF, Postscript.

-renard

Re:Why?

[rocketlawyer]

The fundamental root of the problem is that time is one of those concepts that we all THINK we understand, but frequently we are talking at crossed purposes. Here the problem is a tension between those who use time to measure the duration between two events and those who use it in its more historically traditional role as a metric describing the orientation of the Earth.

Initially the precise measurement of time was the province of astronomers and ship navigators. Time was fundamentally the measurement of the orientation of the Earth. Time was a function of location. Noon was when the sun was at zenith. If you could know the difference in time measurements at two locations, you could determine the difference in longitudes of the two locations. In order to determine the differences in time systems, mankind developed precise mechanical time measuring systems. The new time measuring systems allowed man to measure the durations between events very precisely.

Eventually man developed atomic clocks that could use the decay of atoms to provide an incredibly stable time reference. However, some time ago, we reached a point where the mechanical time measuring systems became more stable than the Earth's rotation. So the atomic clocks which were counting down seconds very accurately were now getting out of synch with the Earth's rotation which was slowing down (and not smoothly slowing down, either).

Since no one who was concerned with the durations between events wanted seconds that varied in length, which is what would happen if you fixed the varying length of the day at 86400 seconds, the concept of using seconds of fixed duration (based on an atomic standard) was developed. The ever accumulating count of these seconds is TAI (Time Atomique Internationale aka International Atomic Time). The time which represents the orientation of the Earth is Universal Time (UT). (This is a simplification, there are a number of subtle variations on UT that I'm not going to go into, but which aren't important for the purposes of this discussion.)

If left alone, the difference between UT and TAI would grow. So, many years ago the concept of UTC (Universal Time Coordinated) was invented. This time standard uses the standard TAI second, but at irregular intervals, an additional second may be added (on either June 30th or Dec. 31st) to always keep UTC and UT to within half a second of each other.

The bottom line is that for people who have to deal with durations, especially long durations, having those irregular additional seconds is a bookkeeping pain and for those who need to be very concerned about the orientation of the Earth, a half second isn't nearly accurate enough. The latter group are undoubtedly using much higher resolution correction data that is produced by the IERS (International Earth Rotation Service). For most civilians, the fact that noon is shifting off by a second every couple of years just doesn't matter. (Especially since the railroads introduced the concept of time zones a little over a hundred years ago, which means that the sun is rarely at zenith when the clock says its noon.)

A lot of people in the field have questioned for some time whether in the era of modern computers where using the higher resolution IERS corrections is trivial, the leap second has any use. Now it may finally be going away.

Now if you want to get really esoteric, here is something to ponder: For astronomy and celestial mechanics, time is defined as the independent variable in the equations of motion of the universe. For physicists and those who use atomic time standards, time is defined as the independent variable in the decay of atomic particles. Noone, to my knowledge, has ever been able to detect a difference in these two independent variables, but it is not a given that they are the same.

For those who'ld like to know more, the University of Texas teaches a graduate level course in the Aerospace Eng. Dept. on the "Determination of Time".

Re:Why?

[darthtuttle]

Because while the day is 86400.002 seconds long (on average) it's getting longer. About 170 years ago the day averaged 86400.000 seconds long. In 170 years it shoudl be about 86400.004, though the slowing down is caused by the moon, which is moving away from us, so it's effect will get less and less (though probably not that fast) but it could be as little as 86400.003. The point is, the second is defined by one measure and the day another, and we are trying to cram the two measures together when they don't have a linear relationship.

Obligitary Hitch Hiker quote

[Zerbey]

Time is an Illusion. Lunchtime doubly so.

Re:Obligitary Hitch Hiker quote

[Bob McCown]

Gotta love Hitch Hiker stuff

Except when the guy you just stopped for hasnt showered for a week...

Time measuerments that make sence...

[Eric_Cartman_South_P]

I've said this before, but I think Maxtor Hard Drive MTBF rates and Iomega tape drive MTBF rates are good, consistent, short time measuerments (both very shitty products that fail reliably).

Me: Wanna go have sex?
Hot Girl: OK! When?
Me: I'm on lunch break in 3 Maxtors and a Tape.
Hot Girl: I'll pay for the Hotel room.

Re:Time measuerments that make sence...

[Wanker]

The problem is he's finished in only half a Maxtor...

For Those Interested About Leap Seconds In General

[PipianJ]

This site may be more helpful, especially in clearing up some of the problems with leap seconds (and their ultimate creation of an offset from both TAI and GPS time)

The easiest solution to all this is

[happyhippy]

SPEED UP THE EARTH!

I propose we keep the earth spinning at a constant rate by detonating thousands of nukes at certain places once every four years. This will produce a Catherine Wheel effect and the earth will speed back to its original spin rate.

I am going to patent this idea but I fear itll be 500 years before I get it processed.

Re:The easiest solution to all this is

[panaceaa]

No, we should constantly redefine 'a second' so there's always 24*60*60 of them a day. This would benefit hardware manufacturers greatly.

You know your 25 MHz computer from 10 years ago? Guess what, now that days are longer, it's 25.001 MHz!!!

Leap second: history and possible future

[PickaBooga]

This is the link to a summary of the issues involved, written at a slightly less technical level.

(don't have to pay, don't have to register, etc.)


http://www.cl.cam.ac.uk/~mgk25/c-time/metrologia-l eapsecond. pdf

an attempt at a summary....

[Malor]

If I understand what I read correctly, essentially the problem they're trying to solve is this: the Earth's rotation is slowing, but they can't predict exactly how much it's going to slow at any given time. It is a real, physical thing, and while they can model its orbit with extreme and unchanging accuracy (things are widely separated enough that the mathematical abstractions work fine), modeling its rotation isn't really possible. There's all sorts of liquid sloshing around everywhere, both liquid water on the surface and molten rock in the center. All they can do is measure it, and every once in awhile, determine that sunrise is happening just a little late.

There are two major timekeeping systems: TAI, which is "absolute time" and is never adjusted, and UTC, which is "civilian time". Because UTC is used by normal people, they try to keep it synced to the Earth's rotation, which in theory at least makes it more useful for us mere mortals. (knowing that the sun will rise at exactly X time on X date at sea level, for instance.). So, gradually, UTC diverges from TAI, because one rotation of the Earth is just a little longer than 24 hours, and over time this divergence adds up to be greater than a second. When it's getting close, they add a leap second. These additions are not at regular intervals, because they can't predict exactly when any given second should be added.

There are occasional problems when they add the leap seconds (programs that don't expect 61 seconds in a minute, for example), or programs that don't realize that there are X number of seconds (15 or so?) that simply didn't exist since 1970. (sometimes this stuff matters).

Thus, they're debating about doing away with leap seconds altogether. One possible substitute is a 'leap hour' every thousand years.

It seems like a rather anal-retentive thing to argue about, but these people are paid to be precise to a degree we can't even imagine.

A worthy slashdot story. This is serious geekery. :-)

Re:an attempt at a summary....

[Tackhead]

> Thus, they're debating about doing away with leap seconds altogether. One possible substitute is a 'leap hour' every thousand years.

Why not?

Asshats from the Industrial Revolution days make us do a frickin' "leap hour" twice a year anyways, one of which violates causality. Fuckin' Daylight Savings Time.

What drooling asshat decided that it'd be a good idea if, every year, there was one day when everyone's heart/respiration rates slowed down to one beat/breath per hour, and about six months later, these same people should be able to start a 20 minute download that finishes 40 minutes before it started?

Fine if you've got a black hole nearby for the former, and fine if you can travel faster than light for the latter.

The day we have those technologies, fine. Until then, no, no, no, no, no, these are bad, bad, bad, bad, bad ideas.

Re:an attempt at a summary....

[Noren]

In college we had the tradition of the 'Negative time Tommy's run'. Tommy's was a hamburger joint open all night. We'd leave at, say, 2:30 AM, go eat supfast (or whatever a meal eaten at that time is called) and return to campus before we left, at 2:20 AM.

Might as well make an event out of our nonsensical system of labelling the current time.

Re:an attempt at a summary....

[pyrrho]

"all please stand witness, you will be amazed.

watch while I move the SUN ITSELF BACK in the sky, ONE HOUR!

there, done!"

"hey, he didn't move the sun, I saw him, he just change the time setting on the clock!"

"did not"

"yes you did"

"not at all, the sun is now in the wrong place, a full HOUR different from where it was yesterday at this time."

"It is not."

"is too"

and so forth.

Re:an attempt at a summary....

[Citizen of Earth]

There are occasional problems when they add the leap seconds (programs that don't expect 61 seconds in a minute, for example), or programs that don't realize that there are X number of seconds (15 or so?) that simply didn't exist since 1970. (sometimes this stuff matters).

I think that the present UTC compromise is quite reasonable. In almost all civilian systems, including non-real-time computers (like the one you are using right now), you really don't need perfectly constant real time and they are probably usually off from the correct time by a few seconds to a few minutes anyway. The leap second is handled seamlessly as just regular clock skew. I've never seen a PC that didn't gain or lose about 30 seconds a day anyway. (That's really pathetic when you consider what a $5 watch can do.)

If you have some kind of real-time system, then just use TAI. It's about 35 seconds off from UTC. I'd like to have a civil time that is closely synchronized to the real world (UT-1).

AFAIK, the loss of time is fairly predictable since a rotation day is about 86400.002 seconds long so a leap second accumulates about every 500 days. They have a leap second about every 1.5 years (on June 30 and December 31).

precision timekeeping is real interesting stuff

[foog]

And why do we care?

Read the article!

It's important for systems programmers, and lots of folks here are at least systems programming fanboys.

It's important for navigation. Yeah, that includes your GPS toys.

It's important for a number of scientific disciplines, including a number of subdisciplines of radio astronomy.

It's also really interesting that the change in the Earth's rotation can't yet be predicted with enough accuracy to set a schedule in advance for adding leap seconds, but must be measured. This is relatively prosaic stuff that's nonetheless at the limits of our current understanding. Doesn't anyone get excited or curious about science anymore?

Re:precision timekeeping is real interesting stuff

[Tailhook]

This is relatively prosaic stuff that's nonetheless at the limits of our current understanding.

So we don't know why the Earths rotation is slowing? I'll bet we do. It's probably the net result of several factors, most if not all of which are understood. The problem is that we have no way to collect enough data to predict the amount of slowing.

The orbit of our Moon is slowing growing larger also. Something to think about; which is more difficult? Speeding up the Earths rotation or stopping the Moon from running off?

Of course, the solution to all this is really big rockets, but we've got plenty of time for that. :)

Accuracy isn't everything...

[stefanlasiewski]

And just think, if no leap seconds were added since 1972, you'd be having your Noon Lunch at 11:59:38!

Oh the horror... :)

Accuracy isn't everything...

Leap seconds and leap years, keep em

[zarthrag]

first of all, I think it's important to keep on track with time, it's not like we don't have the technology to keep it up. Isn't it amazing that we can even develop the concepts in the first place? Leap years have been incorporated for awhile now, it keeps the seasons from drifting to some "other" part of the calendar. (Winter in July anyone?) Daylight savings wasn't invented to annoy people or make people appreciate the season by forcing you to be awake earlier. It saves energy by having people awake during the daylight hours. This means you're more likely to open a window than cut on a light, and go to bed while it's dark out. While leap seconds are comparatively minute, it's just maintence. (Y2k is an example of what happens when we don't think far enough ahead). I think modern-day timekeeping is the result of centuries of work. It started with us observing the sun, then the stars, and now the earth itself. Needless to say, timekeeping ought to be an exact science. Until we find something more reliable of deserving to serve as a time reference, we ought to keep our ears to the ground. We do happen to live here, and I think the Earth deserves to set the pace.

coding for leap-seconds

[Anonymous Coward]

requires a lookup table and regular (like every
two weeks) network connections to the Navy's
leap second table server to detect updates,
and the software needs to parse the table and
account for the update if and when it occurs.

Since we have not had a leap second update since
1999, it has meant there has been lots of time
for folks to get complacent and ignore the update
checks, so most recent code that handles leap
seconds is trouble waiting to happen.

I will be very happy when leap seconds are put
to bed.

What are leap seconds?

[Phroggy]

Leap years work like this:

One year = the time it takes for the Earth to revolve around the Sun.
One day = the time it takes for the Earth to rotate on its axis.

The problem is, there are really about 365-1/4 days in a year - it doesn't work out evenly to 365 days. So, every four years we add an extra day (Feb. 29), and then it all averages out. Otherwise, if we only had 365 days in a year, over many years seasons would start getting earlier and earlier on the calendar.

One day = the time it takes for the Earth to rotate on its axis
One second = the time it takes for Cesium 133 to oscilate about 9.19 billion times (because it's something constant we can measure)

The problem, again, is that there aren't exactly 86400* seconds in a day. So, we add leap seconds periodically to account for it. As I understand it, this isn't necessarily done at fixed intervals, but rather whenever it's decided that it needs to be done. The Network Time Protocol used to synchronize clocks over the Internet supports leap seconds; they can be announced over NTP in advance, so everybody adds them at the correct moment.

Why is it important? It's not important to most people, but computers like things to be precise and accurate for various reasons, and that means we have to agree on exactly what time it is.

* BIND now lets you write "1d" in a zone file, but how many of you still have this number memorized? ;-)

This doesn't make any sense at all

[rrkap]

A slashdot reader having sex with a hot girl????????

Either the poster's definition of hot, girl or sex is seriously out of whack.

Time zones

[cperciva]

The stated problem with leap seconds is that some software gets confused by them. Guess what? That same software probably gets confused if the time zone changes, or when it moves into daylight savings time.

The Right Way to solve this problem is for computers to work with TAI internally, and treat the difference introduced by leap seconds as part of the time zone, for human consumption only. Instead of defining PST to be UTC - 08:00, define PST = TAI - 08:00:22.

Computers can keep their straightforward time system, humans can keep our astronomically synchronized system. No need to lose either of those qualities.

Umm.. yeah.

[blenderfish]

Hmmm..

"matter of international significance"

Hmmm... I know!

echo "matter of international significance" | perl -p -e 's/t..n[^s]+//';

Ahh. Now *THATS* more like it.

I know who's fault this is!

[buyo-kun]

A bird, a plane, No SUPERMAN

When he messed around with the Earth's rotation to save Lois Lane, he got lazy and messed it up by a tiny bit. Now look whats happened, we're off by a couple seconds now.

This is what happens when you get an alien to do a human's job.

Oh, but it is...

[smartfart]

"It is a matter of international significance."

It's about time someone did something to correct these errors.

/me runs off before he gets thwapped.

(it's funny, go ahead and laugh, willya?)

i got affected by leap second

[u19925]

seriously, i did! during one of my scientific experiments (I believe it was in Jun-93), they added leap second in the middle of my experiment. The data taken from various places could not be combined together, since they didn't know at what time, leap second was adjusted at which place. So we had a 24 hours experiment on 300 million dollar equipment failed and 100's of manhours were lost in the process.

Re:i got affected by leap second

[u19925]

no i didn't design one bit of the equipment. the equipement belongs one of the national labs and the only lab of its type in the world. the equipment was newly designed with lots of new hardware and real time software. have you heard of 350 GByes of uncompressed data on a single tape? well there were 11 of them in the experiment a decade ago! they obsoleted them more than a year ago! these data on each tapes are marked using time stamp (since the tape drives are located from east coast to hawaii). in order for the experiment to succeed, each block of data recorded at the same time must be combined. there is no independent way to say that the data tracks on two tapes are aligned other than the time stamp. you get meaningful data only if close to all the data are aligned perfectly (to within few microseconds). processing of these data is too expensive too. so trial and error is ruled out. basically, the committee felt that it wasn't worth salvaging the data and I got one more day to use this equipment.

one way to look at this experiment is like this. you have a very faint object that you are photographing. you also want 360 degree view and are using 10 cameras at different angles. Due to shaky-ness, you can't use long exposures. So you use multiple photos which you later combine in your computer. Assume that the object was moving randomly but you know the exact motion. Now if you forget to remember what time, each frame was taken, there is no way to do motion compensation and hence no way to superimpose the frames. now if your computer was too slow to superimpose the images, it may not be worth doing trial and error.

Why Stop at Leap Seconds?

[the eric conspiracy]

It seems to me that we should get rid of the concept of seconds altogether. The second was devised in the Sumerian culture, along with such bizarre ideas as a circle having 360 degrees.

The French of course stole the concept of decimalization from Thomas Jefferson and applied it to a variety of measurements, but failed to carry it to a good conclusion by decimalizing time (it seems everything French starts off well but is never really completed).

It seems to me that real progress should be made by dividing the day up into decimal units of time, and the circle into decimal units of arc, thus eliminating the second as a unit of measure.

Re:Why Stop at Leap Seconds?

[grolim13]

Wasn't the razor invented by a French woman?

I thought it was William of Occam...

Enough Earth-centrism!

[Okonomiyaki]

With a manned mission to Mars possibly less than 20 years away, shouldn't we start looking at timekeeping systems that aren't tied to this rock?

Re:Enough Earth-centrism!

[GigsVT]

I know you were probably joking, but since you were modded insightful, I guess I should reply, if for nothing other for the sake of the people that modded you up.

There really isn't a concept of time unless it is relative to something. Think about it.

Re:Enough Earth-centrism!

[Idarubicin]

With a manned mission to Mars possibly less than 20 years away, shouldn't we start looking at timekeeping systems that aren't tied to this rock?

Actually, it's been done. In Kim Stanley Robinson's Red Mars, a Martian colony did adopt a clock customized for the local conditions.

The Martian day is twenty-four hours, forty minutes long, roughly. Mars kept a twenty-four hour clock, with hours, minutes, and seconds remaining the same length. The colony then added a forty minute period (the 'timeslip', if I remember correctly) after midnight. During this period the clocks (all digital) would stop for forty minutes at 24:00, then resume counting at 0:00 the follwing day.

Though neat for dramatic purposes, I would think it more useful to simply run the clocks for a short twenty-fifth hour, forty minutes long. Days could be counted--forget months--for a total of 669 Mars days per year.

The single most useful thing about such a technique is that it preserves the length of the second. Since any human presence on Mars would likely be a scientific outpost for many years, maintaining the second is very important for many measurements. I don't want to have to deal with a kludgy factor of 1.03 in comparing times.

Where it went wrong

[Pflipp]

There used to be a time that a second was something that would fit 24 x 60 x 60 times in one day -- no matter how long the day was. Nowadays a second is something like this-and-that many vibrations of some atomic particle thingy.

So maybe we should just stretch the number of vibrations of the particle thingy a little, instead of adding extra seconds to days :-)

Big Deal

[teslatug]

OK, we can slashdot a webiste, surely we can fix this. Ok, on 3 let's all start running west. 1...2...3...

running though is not so popular among this crowd...

The science behind the length of a day

[Noren]

Check out this presentation. It describes the methods currently used to accurately determine the rate of the earth's rotation, and how they've been able to use historical accounts to get earth rotation data points- if they have a record, for example, that there was a total eclipse in a certain city in Babylon at local noon on January 1, 1000 BC, they can use the orbits of the earth and moon (which are well-modeled over that time frame) to figure out when in UTC that eclipse must have happened, and compare the two.

It looks like the day is getting an average of 2ms longer per century, but it fluctuates 4-5ms away from that on a decade timescale plus some shorter-term noise.

leapsecond.com

[jeffmock]

A really interesting guy on this topic is Tom Van Baak, the fellow that runs leapsecond.com. As a measure of the level of obsession a person can obtain, this guy has multiple cesium frequency standards, but he had to go out and buy a crazy russian hydrogen maser so he could get better than a microsecond a year accuracy. He's also got some interesting information about the leapsecond debate on his website.

Me, I'm a simple guy, I just need to keep NTP locked to a couple of microseconds to sleep well.

jeff

Fix it in 397 years

[smoondog]

Here's an idea, why not fix it on those wierd years, without leap years. For example, 2100 is not a leap year, even though it is divisible by 4 (because it is divisible by 400 and 100). Since many computer programs won't handle that correctly, on those days, adjust for the missing seconds (a few minute change).
Kill two birds with one stone, so to speak.

-Sean

I'm divided

[Progman3K]

On the one side, I don't like the idea of time being shifted around like that because it could upset my schedule, what with a tenth of a microsecond popping up like that every year, but on the other hand, if we wait until there is a full second accumulated, it could be really hard to decide what to do with it...
I mean, do I go on vacation, read a book, learn a new language? What to do with the extra time is just too huge a responsibility.

My Proposal for Leap Things...

[telstar]

Leap year, leap seconds, leap minutes, daylight savings time ... change all of this stuff so that it cuts a year/seconds/minute/hour out of my workday, and you'll get my vote. Losing an hour of sleep overnight on a Tuesday does nothing for me, but skipping that mid-Monday meeting would be a God-send.

America Is To Blame

[istartedi]

America is to blame! We are only 5% of the Earth's population, but we use 80% of the angular momentum. Scientists have warned us for years about global slowing, but big business Republicans, and Democrats with large angular momentum consuming projects in their districts refuse to address the issue. The only viable solution is to make papier mache puppets and parade them down Pennsylvania Avenue.

Re:America Is To Blame

[Idarubicin]

America is to blame! We are only 5% of the Earth's population, but we use 80% of the angular momentum.

It's the failure of the world's industrialized nations to use renewable power sources. By drilling for oil, millions of tons of heavy crude are removed from the the depths of the earth and brought to ground level. Since angular momentum is conserved, the earth's rotation slows slightly to compensate for the now-larger moment of inertia. Extraction of metals from mines also contributes to the problem.

Granted, we have in part compensated by dumping large amounts of waste into deep parts of the ocean, and cutting down trees--but it's not enough! We need to begin a massive campaign to raze the forests and dump mercury and lead into oceanic trenches. Hopefully, we will one day be able to restore the Earth's rotation.

Because

[autopr0n]

The amount of time it takes is not constant. All we can do is mesure the rotation and let everyone know when it's changed.

The real problem

[metamatic]

Right. The real problem is that lots of people who write code dealing with times and dates do a really crappy job. Some piece of software breaks every leap year, every time we change to daylight savings time, every time the dates of daylight savings time change, every time there's a leap second, every time you move your computer across time zones, every time a year divisible by 4 isn't a leap year... Just last month I reported a bug in a library function in a well-known software product, and had to explain to the developer that no, we weren't on DST yet, but Australia was.

So this leap second debate is really just a cunningly disguised way of talking about the crisis of software quality. The fact that a lot of software can't deal with 23:59:60 is the same problem that causes a lot of software to fall over when there's a February 29th.

Re:leap seconds are evil

[Russ Nelson]

leap seconds are only evil when you try to commingle UTC and TAI. If your system operates on a straight TAI, then leap seconds become a presentation issue right along with time zones and daylight savings.
-russ

Leap leaps

[gad_zuki!]

> SPEED UP THE EARTH!

I wholeheartedly agree. We can shed some mass temporarily and help the earth spin faster by "leaping for leaps." Every few months or so everyone on a given continent will jump up at the same time. I'm sure it'll all work out just fine. Organize a "leaps for leaps" chapter in your town today.

Examine the Purpose of Timekeeping

[m1a1]

I think that the removal of the leap second is a big mistake. Sure any noticeable changes will be extremely gradual, keeping time has more purposes than just knowing what time to leave for lunch. If we read about cowboys fighting at high noon, we know what it is. If we read about Paul Revere's midnight ride, we know that it did indeed happen at night.

Removing the leap second makes most history recorded with reference to time of day pretty useless. Noon is defined by most people as the time that the sun is in the middle of the sky. Let's keep it that way. If method of keeping time based on exact seconds from one point in time to another (which is actually pretty useless for most things that happen within timeframes longer than a couple of minutes) then let a separate system be designed for it. Start reading off an atomic clock and never account for leap seconds, but don't screw up the rest of the world to please a few.

Re:Examine the Purpose of Timekeeping

[Idarubicin]

Noon is defined by most people as the time that the sun is in the middle of the sky. Let's keep it that way.

Too late. In most places, local solar noon hasn't been used as a time standard for more than a century. Depending upon where you live within your time zone, the local solar noon can be different from standard time by a half hour or worse--and I'm not going to mention the impact of Daylight Saving Time.

Correcting--or not correcting--the time through use of leap seconds makes a difference of less than half a minute per century. The leap second correction is too coarse for almost any scientific work, and much too fine for the average person on the street.

Why not have a leap minute, where necessary, once every two or three centuries? It will still be dark at midnight, and we reduce the hassle of dealing with time discontinuities by a couple orders of magnitude.

But don't stop The Core!

[GuyMannDude]

I wouldn't be so quick to suggest tampering with the earth's rotation. I recently saw a very intellectual documentary about what can happen if the earth's core ever stops rotating. Birds would fall from the sky, people with pacemakers would keel over dead, and entire football stadiums would be electrocuted by superstorms. All sorts of crazy shit that you wouldn't expect happens when crazy scientists start messing around with the earth's rotation.

GMD

My sex life!

[zackeller]

No! If they get rid of leap seconds, that'll cut my sex time in half!

Old saying

[mcrbids]

All this techno mumbo-jumbo is just an overly verbose representation of an old saw:

A man with a watch always knows what time it is. A man with two watches is never quite sure...

IERS (International Earth Rotation Service)

[merlyn]

Wow. I didn't realize we had advanced to the point where we had an international coalition just to keep the earth spinning!

Is France a member?

Do they take requests? ("I'd like an extra long sunset this Friday night... I have a date!")

Re:IERS (International Earth Rotation Service)

[darthtuttle]

Why do I find this wildly humourous considering your run stonehenge.com... ...just move the rocks around a bit.

several timescales

[darthtuttle]

There are several timescales. There is already one that does not have leap seconds, and one that does. What is important for the average person is that when the beep, beep, beeeeeeeeep goes beeeeeeeep it's the same for *all* people. While 22 seconds isn't a big deal for most people, it's a huge difference in a lot of other areas from financial trading to shipping. There's a hint of the fact that a USBN (submarine) hit something because a leap second got inserted in to a clock that no one was prepared to handle and they went a second to far.

The leap second reconizes the fact that the "second" is defined in terms of particle physics (a quantity of state changes) which is very stable (it's always going to take the same amount of time for the same quantity of state changes), where as the idea of time really comes from the cosmos. When the sun is directly overhead it's 12:00.

Where the earths orbit around the sun is very stable, 265.24 days, the rotation of the earth is very unstable. In fact, there's a provision (though never used) to remove a second from the day! The speed of the rotation is constantly changing. Over the long term it's pretty stable with a stable decay, but in the short it could be necessary to add a second rather quickly to keep the civil time within .9 seconds of cosmic time.

The long term average is that we need to add a second to the day about every 18 months, but we haven't needed a leap second since the end of 1998 (over four years!) so in the short term the stability of the earths rotation is low compared to the order of magnitude we measure.

In order to handle this a desicion is made every six months as to a new leap second at the end of June or December (or to remove a second). This is a problem because some systems can't handle the addition of a second on six months notice such as the submarine!

One proposed solution is to allow UT1 (cosmic time) and UTC (civil time) to be out of sync by as many as 10 seconds. This would allow for ample time for warnings to be produced and everyone to know exactly what is going to happen and how to handle it. I don't know if the protocol would add 10 seconds at once, or warn everyone a few years in advance that a second is going to be added at several different points in time.

One interesting side note. Most computer systems don't handle leap seconds. Time keeping software slows the computers clock down (since it's important not to have events which have happened (past) in the future (future). This means that if your measuring anything else based on time that measurement is going to be wrong. The theory being that the accuracy in what time it *is* is more important than what time it *was*. The reason I bring this up is that time is something that can be measured with amazing percision, where as other things can't be measured as well. If you can convert one measurement to time you can measure it more percisely. For example, how fast does the ISS move? If you know it's altitude by measuring how long it takes to bounce a light off of it, and you know how long it takes to get from A to B (or from A to A again), you know how far it moved and how long it took to move and voila, speed, all by measuring time. If a leap second got thrown in while you weren't paying attetion during your measurement, your speed will be wrong.

Great news!

[kavau]

...but earth rotation is slowing down.

This is the best news I've heard in a very long time! I'm sure I'm not the only one who thinks that both day and night are way too short. How long do we have to wait until the day will be 25 hours? Aaaahh... I'm looking forward to that extra hour of sleep!

Why do electronics have to use the same "time"?

[Anonymous Coward]

Posters seem to broadly agree that we use time in 2 ways: 1, as humans, to "tell the time of day", ie relating the position of the sun in the sky to a time of day, which should not change, and 2, to measure a time difference between 2 events, which may have nothing to do with the sun or times of day. Clearly, for the first application, leap seconds etc. are important to eliminate drift. However for the second use of clocks leap seconds don't matter. So why not use Julian dates (number of metric seconds since some datum) for stuff like GPS, atomic clocks etc. and keep normal times with all the quirky leap seconds for "human-interface" use? After all, we don't find out the time of day from a GPS so why does it need to use minutes, hours or days? Julian timekeeping is already in widespread use in astronomy for "interval between 2 events" uses so I don't see why it couldn't be used in other such applications. We could even have a nice standards-based libtime to convert between the two.