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Science

The Future of Leap Seconds 429

Posted by michael
from the stuff-you-thought-you'd-never-think-about dept.
@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."
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The Future of Leap Seconds

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  • Why? (Score:5, Interesting)

    by k-0s (237787) on Friday April 18, 2003 @05:53PM (#5762546) Homepage
    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? (Score:2, Interesting)

      by joe_bruin (266648)
      the trains are now running on time -- metric time.
    • by stefanlasiewski (63134) <slashdot&stefanco,com> on Friday April 18, 2003 @06:13PM (#5762655) Homepage Journal
      And just think, if no leap seconds were added since 1972, you'd be having your Noon Lunch at 11:59:38 [nist.gov]!

      Oh the horror... :)

      Accuracy isn't everything...
    • Re:Why? (Score:2, Funny)

      by aztektum (170569)
      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? (Score:5, Informative)

        by Anonymous Coward on Friday April 18, 2003 @06:52PM (#5762813)
        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? (Score:5, Interesting)

        by Guppy06 (410832) on Friday April 18, 2003 @08:22PM (#5763116)
        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? (Score:5, Informative)

          by renard (94190) on Friday April 18, 2003 @11:54PM (#5763804)
          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 [navy.mil], Postscript [navy.mil].

          -renard

      • Re:Why? (Score:5, Informative)

        by rocketlawyer (535374) on Saturday April 19, 2003 @12:36AM (#5763935) Homepage
        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? (Score:3, Interesting)

      by pVoid (607584)
      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

    • Re:Why? (Score:3, Informative)

      by Vellmont (569020)
      I wondered this too, and you have to dig a little bit to find the answer. It seems most people don't like it because the software they use is often a pain in the butt to adjust for the leap second. Check out the survey here [obspm.fr] that seems to give some decent answers to why leap seconds suck for some folks.

      Here's an example of a complaint:


      Answer:
      Because time discontinuity causes a number of problems in handling time-stamped geophysical data such as seismic.

      Because time discontinuity caused by the leap sec

  • by Anonymous Coward
    "So, what do you do?"

    "I am a keeper of the time."

  • I hope... (Score:5, Funny)

    by MoonshineKid (615121) <pogo118@ea r t h l i n k.net> on Friday April 18, 2003 @05:53PM (#5762553)
    I hope this means we get an extra second of February every four years. I love February.
  • by lightspawn (155347) on Friday April 18, 2003 @05:54PM (#5762557) Homepage
    Considering that some programmers (of commercial software, no less) have no idea HOW TO CHECK IF A YEAR IS A LEAR YEAR, I fear this is going to be no less catastrophic than Y2K, perhaps even a cataclysm of Y2038 proportions!

    Excuse me while I stock up on food, medicine and ammo.
  • WWV (Score:5, Informative)

    by io333 (574963) on Friday April 18, 2003 @05:55PM (#5762562)
    Everything you ever wanted to know about precise timekeeping, from the keeper himself! [bldrdoc.gov]
  • by Blaine Hilton (626259) on Friday April 18, 2003 @05:55PM (#5762565) Homepage
    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.

    • by Guppy06 (410832) on Friday April 18, 2003 @07:28PM (#5762936)
      "With the increasing amount of precision in today's timekeepers these problems seem to be cropping up more and more."

      What's this "today's precision" bullshit? We've been having this problem for thousands of years.

      For centuries, peoples dickered back and forth about how many 28-day lunar cycles ("months") were in a year. Some said 12, some said 13. The concept of fractions apparently escaped these simple folk.

      Then the Romans came along. Not to be daunted by silly things like "reality," they declared that the lunar cycle was really 30 days, and that there were exactly 10 of those months in a year. While they were at it, they delcared pi to be exactly 3.125. To make things work out a little better, they threw in some extra days between a few months whenver they felt the need. The Latin names for these periods translates roughly to "Not really a month."

      That got real old real fast so they threw in two more "real" months, and juggled around the lengths of the months just because they could (They're Romans, they ruled the world, yadda yadda yadda).

      That one actually lasted a few centuries, at which point they started to admit that things were still screwy (in the sweltering heat of January), which was also the same time when some guy named after a salad was thinking he was Alexander the Great. The Senate told saladm boy to go fix things (apparently smacking cheese-eating surrender monkeys around qualifies one to make a calendar). Lo and behold he did, declaring that a year was 365.25 days long (ie. every fourth year had a full extra day). Ever humble, he took the time to re-name a month after himself. Feeling insufficient in some department, he also shifted around some days so that his own personal month was longer than most.

      For a group of people that had no concept of zero, this system worked pretty well for a millenium or so, when it became obvious that things were getting screwy again. This time, the folks in Rome asked some guy with a funny white hat named Greg to help sort things out. Apparently not as experienced in invading France as salad boy was, he decided he had to plagiarize somebody else's work. He found some insane scribblings from some Poloc kook who figured out that a year was "really" 365.2425. Because the Poloc was loony (he said the earth went around the sun, of all things!), Greg felt comfortable with taking that number without admitting where he found it.

      The system work, but the folks Greg worked with had a bit of a bad reputation at the time. To the west, there were a bunch of political crackpots who called themselves "Complainers" or something like that, and to the east there were a bunch of people in even funnier hats than Greg's who all spoke Greek. So it took a little bit of time for "Greg's Nifty Calendar" (why name a month after yourself when you can rename the whole damned calendar?) to catch on, which is why nobody can figure out when Washington's birthday is and why the October Revolution took place in September.

      And even now there are all sorts of people from Newton to Einstein that say that even that calendar is screwed up! Greg's plagiarized number was off by 0.0003 days! That's almost 26 seconds! Heck, after a few thousand years that's a hole big enough to drive a Mack truck through, and then where will we be?

      "With our global economy (weather we like it or not) times need to be synced across the world."

      Between the Greek-speaking folks still thinking Greg was the anti-Christ and two groups of people blowing themselves up in the Middle East still trying to make the whole lunar cycle thing work out, we can't even agree on what day it is!

      Leap second, no leap second, it doesn't really matter to me. I'll always have NTP.
  • by dobedobedew (663137) on Friday April 18, 2003 @05:57PM (#5762574)
    We don't even do Daylight Savings Time here in Indiana. Whatever the rest of the world decides, we will resist - I can't wait to see our citizens and politicians get in an uproar over this!
    • by tap (18562) on Friday April 18, 2003 @06:31PM (#5762725) Homepage
      Actually, you do use daylight savings time in Indiana [mccsc.edu]. There are eleven counties that are on central time and use DST, five counties that are eastern time and use DST and 76 counties that are eastern time and don't use DST. So Indiana has no less than three different time zones. At least they don't have multiple timezones per county.

      Given Indiana's history with keeping time, probably half the counties will participate and half won't. And some will just switch to the Mayan calander and be done with it.

    • by Max Threshold (540114) on Friday April 18, 2003 @07:50PM (#5763019)
      I think it's great that we don't use DST here. Everyone curses it, and I know from experience (having moved elsewhere for a while) how it screws up your circadian rhythms. I felt like I had jet lag for a month.

      A few years ago somebody was running radio commercials here to support a bill that would have put us on DST. The tug-your-heartstrings appeal was that "there are two states that don't use DST: Arizona because of the heat, and Indiana because of special interest groups" (always the Bad Guys here in Indiana.) who want our kids to wait for the school bus in the dark.

      Funny because DST makes it darker at any given hour of the morning, and everybody knows that the "special interest groups" who came up with DST in the first place are commerical interests who wanted to extend their business hours. Either the writers of that commercial were really, really stupid, or it was a brilliant piece of social engineering. Either way, I don't think Indiana will be adopting DST any time in the near future.

  • by Zerbey (15536) on Friday April 18, 2003 @06:01PM (#5762596) Homepage Journal
    Time is an Illusion. Lunchtime doubly so.
  • by Eric_Cartman_South_P (594330) on Friday April 18, 2003 @06:01PM (#5762599)
    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.

  • by PipianJ (574459) on Friday April 18, 2003 @06:02PM (#5762604)
    This site [navy.mil] 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)
  • by happyhippy (526970) on Friday April 18, 2003 @06:05PM (#5762615)
    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.


  • 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

  • by Malor (3658) on Friday April 18, 2003 @06:08PM (#5762630) Journal
    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. :-)
    • by Tackhead (54550) on Friday April 18, 2003 @06:28PM (#5762711)
      > 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.

    • It seems like a rather anal-retentive thing to argue about...

      Yeah. Just a little related story, if anyone's interested...

      A few years back, I was working at a software firm that dealt with satellite radar imagery. The software calculated the satellite's lat/long position by extrapolating from a known time and position right after launch, to the time when the data was captured. Some of these satellites had been in operation for over ten years.

      At the time, I was fixing it up to be Y2K compliant. I d

    • 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 proba
  • by foog (6321) <phygelus@yahoo.com> on Friday April 18, 2003 @06:12PM (#5762648)
    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?
    • 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 f
  • at around 4 1000th's of a degree for each leap second, it will take a while before it makes any difference; my sundial will be ok.

    We should set our clocks based on the rate that the universe is rotating instead.
  • Then high noon is always high noon.
  • 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 du
  • by 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.
  • by imp (7585)
    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.
    • 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
  • by Phroggy (441) <slashdot3NO@SPAMphroggy.com> on Friday April 18, 2003 @06:24PM (#5762698) Homepage
    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? ;-)
    • So why not redefine one second to equal 1/86400 the time it takes for the Earth to rotate on its axis? Or alternatively, change the number of oscilations of Cesium 133? It seems like a much more elegant solution than these crazy leap seconds.
      • Because (Score:3, Informative)

        by autopr0n (534291)
        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.
  • Time zones (Score:5, Insightful)

    by cperciva (102828) on Friday April 18, 2003 @06:35PM (#5762742) Homepage
    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.
    • The real problem (Score:3, Informative)

      by metamatic (202216)
      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
  • Just wait until the galactic standard week goes into effect.
  • Umm.. yeah. (Score:2, Funny)

    by blenderfish (156901)
    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.
  • GMT is evil! Cubic time is only real time. Ask Gene Ray [timecube.com]!
  • by buyo-kun (664999) on Friday April 18, 2003 @06:43PM (#5762785)
    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.
  • by u19925 (613350) on Friday April 18, 2003 @06:49PM (#5762801)
    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.
    • I'm amazed that you spent 300 million dollars and hundreds of hours designing an experiment that couldn't tolerate 1 second worth of error in the data.
      • by u19925 (613350) on Friday April 18, 2003 @08:23PM (#5763121)
        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.

  • There's a lot of information available at the page linked to by the /. post. It's dense, though. Readers might find this page [noao.edu] a little easier to digest.
  • by the eric conspiracy (20178) on Friday April 18, 2003 @07:06PM (#5762863)

    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.

  • by Okonomiyaki (662220) on Friday April 18, 2003 @07:14PM (#5762894) Homepage
    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?
    • 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

  • Where it went wrong (Score:3, Interesting)

    by Pflipp (130638) on Friday April 18, 2003 @07:20PM (#5762908)
    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 (Score:5, Funny)

    by teslatug (543527) on Friday April 18, 2003 @07:33PM (#5762951)
    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...
  • by Noren (605012) on Friday April 18, 2003 @07:34PM (#5762953)
    Check out this presentation. [ucalgary.ca] 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 (Score:5, Informative)

    by jeffmock (188913) on Friday April 18, 2003 @07:44PM (#5762993)
    A really interesting guy on this topic is Tom Van Baak, the fellow that runs leapsecond.com [leapsecond.com]. As a measure of the level of obsession a person can obtain, this guy has multiple [leapsecond.com] cesium frequency standards, but he had to go out and buy a crazy russian hydrogen maser [leapsecond.com] 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 [mock.com] to sleep well.

    jeff
  • Fix it in 397 years (Score:3, Interesting)

    by smoondog (85133) on Friday April 18, 2003 @08:27PM (#5763129)
    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
  • by telstar (236404) on Friday April 18, 2003 @09:18PM (#5763276)
    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.
  • by istartedi (132515) on Friday April 18, 2003 @09:20PM (#5763288) Journal

    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.

    • 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.

  • by m1a1 (622864) on Saturday April 19, 2003 @12:01AM (#5763831)
    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.
    • by Idarubicin (579475) <allsquiet@@@hotmail...com> on Saturday April 19, 2003 @02:58PM (#5765384) Journal
      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 [greenwichmeantime.com]. 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.

  • Old saying (Score:4, Insightful)

    by mcrbids (148650) on Saturday April 19, 2003 @02:14AM (#5764057) Journal
    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...
  • several timescales (Score:5, Informative)

    by darthtuttle (448989) <meconlen@obfuscated.net> on Saturday April 19, 2003 @11:24AM (#5764582) Homepage
    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! (Score:3, Funny)

    by kavau (554682) on Saturday April 19, 2003 @02:42PM (#5765332) Homepage
    ...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!

We warn the reader in advance that the proof presented here depends on a clever but highly unmotivated trick. -- Howard Anton, "Elementary Linear Algebra"

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