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."

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.

Get rid of 'em

[dirvish]

I personally think the should get rid of leap seconds and leap years. I'm down for keeping it real. Day light savings time is annoying and I really don't understand the point.

Is it time to change time?

[Blaine Hilton]

With the increasing amount of precision in today's timekeepers these problems seem to be cropping up more and more. I don't believe it really matters, except the whole world needs to agree on a standard. With our global economy (weather we like it or not) times need to be synced across the world.

Although if there are going to be changes to the time standards I can always add converters [webcalc.net] to my calculator site for people to use.

Re:Why?

[joe_bruin]

the trains are now running on time -- metric time.

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.

leap seconds are evil

[imp]

Leap seconds are evil. As someone who has spent way too many hours programming high precision time distribution systems to deal with leap seconds, I'd say 'good riddance, don't let the door hit you on the way out. Sites that have to deal with them typically shut down near leap seconds to avoid any glitches. The amount of time wasted on this problem boggles the mind.

I hate them and will not morn their passing.

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? ;-)

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.

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.

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 :-)

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 [physlink.com].

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?

[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: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.

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

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: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.

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.