Slashdot Mirror
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."
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.
Visit www.seriouslythough.com
Time is an Illusion. Lunchtime doubly so.
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.
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)
stuff-you-thought-you'd-never-think-about dept.
I don't like to think about leap years, much less leap seconds...
-------
"In times of universal deceit, telling the truth becomes a revolutionary act."
-- George Orwell
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.
... yeah, there won't be any problems with that.
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-
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.
Too many people farting in one direction.
Thanks, that site is great and very readable/understandable. I definatley think you deserve a 5 - informative
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?
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.
Open source development is my way of competing with the low-cost programmers in India...
Since I find it hard to believe that they're actually going to let our time degrade to the point that noon happens when the clock says 2am of the next day, what exactly do they propose we do? Will UTC be different from the time we'll all use? That way, UTC can be weirdly off, but ours will be ok.
If keeping our noon time happening when noon happens is a priority, I can't think of an easier way to do it than leap seconds.
Then high noon is always high noon.
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...
"Can of worms? The can is open... the worms are everywhere."
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.
Why can't all fpga/microcontroller manufacturers just release free optimizing compilers???
try to realize the thruth ...
....
What truth?
There are no leap seconds
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.
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.
Everyone is always saying "There aren't enough hours in a day". If the Earth is slowing down, we can just add more hours to the day to make up for it. Think of all the lives we will be improving. I mean, I could jack off at least 26 times in a 26 hour day. Yes!
Karma: The shiznight, mostly because I am the Drizzle.
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?
$x='S24;r)>63/* h@<5+oZ)32"5cz';$me='phroggy'x$];
$x=~y+ -xz+\0-Tx+;print$_^chop$me for split'',$x;
A slashdot reader having sex with a hot girl????????
Either the poster's definition of hot, girl or sex is seriously out of whack.
I like my beverages with warning labels!
They vetoed the leap second, didn't they?
I'm confused, as usual.
Does anyone know or care what second the WTC disaster, or Pearl Harbour, or Moon Landing happened at? No. Days matter for history and calculations, seconds do not.
There is nothing significant enough to deserve an exact keeping of seconds, when humanity won't span long enough to have those extra seconds turn into days.
Why slashdot? Why not?
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.
Tarsnap: Online backups for the truly paranoid
You're obviously too young... if you were at least, say, 30, then you'd know that Superman can do this all by himself. No need for nukes. Jeez, kids these days...
"It is a matter of international significance"
I'm gonna have to call bullshit here.
Your post on the other hand, is not very readable/understandable. Let me put it in terms you may understand:
s/definatley/definitely/
Loser.
Just wait until the galactic standard week goes into effect.
"Derp de derp."
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!
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.
It's about time someone did something to correct these errors.
(it's funny, go ahead and laugh, willya?)
Need a Linux consultant in New Orleans?
Is the earth's orbit also slowing? Perhaps at some time the Earth orbitted the sun once ever 365.0000 days instead of once every 365.2425 days.
You can't judge a book by the way it wears its hair.
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 think instead of having nano seconds here and there without any consistent approach, we should store up all our nano seconds until we have enough for a leap YEAR.
So then we can just repeat a year whenever we need to. My vote would be to repeat 1987, that year just had a really good vibe for me.
apt-get install deathstar && deathstar alderaan && echo "You're far too trusting"
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 did some refactoring and put all the date-related code in one place, which was nice. It was also nice because (if I remember correctly), some pieces of code weren't doing leap year calculation correctly.
That was when I learned all about precise time-keeping, and the question of leap seconds weighed on me a little bit. How far off were our lat/long calculations? I'm pretty sure the on-board clock didn't do leap seconds, so we were probably okay, but in some cases, it's possible that the ground receiving station might have inserted the time stamps. Then what? I still have no idea.
In the end, nobody ever talked about leap seconds (including long-time radar experts, which I was not), and furthermore, it was already a reasonably established product, so I just decided it was a can of worms I didn't want to open.
But for a short while, I was cursing the name of those anal-retentive time geeks who had to make life so freakin' complicated for me.
Accountability on the heads of the powerful.
Power in the hands of the accountable.
There's a lot of information available at the page linked to by the /. post. It's dense, though. Readers might find this page a little easier to digest.
Oooh, that must be why my VCR clock always seems to creep ahead! It doesn't account for leap seconds!
Here's an earlier (1994) proposal to do away with leap seconds and suggests among other things, leap hours every few centuries.
Leap hour proposal
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.
Just tell one more word about Syria and i'll find you idiot
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?
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
"We can confirm that Debian does *not* ship the version with the trojan horse. Our version predates it." [CA-2002-28]
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...
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.
Do you have any idea what it takes to attempt high energy matter synthesis?
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
Imagine, the U.S. Navy providing clear, useful, and understandable information!
OK, so the clock people don't want to have to calculate when leap seconds have or will happen when figuring out the time from A to B. And they also want noon to happen when the sun is highest in the sky, and summer to happen on June 20/21.
There is a simple solution:
Build a pair of giant rocket to control the rotational speed of the earth. Then just give it a 'kick' every now and then to do stuff like countering tidal drag and such. You could even get rid of leap years if they were powerful enough!!
NASA isn't even using its last Saturn Vs anyway.... Might as well put them to good use. Or, if that's not enough, we have like 10,000 nukes ready to go.
What's the point of a massive, bloated arms race if you aren't going to use it to impact the rotation of Earth itself??
should be read according to the sun's position. Who needs minutes and seconds?
...by creating and pooling water reserves further from the equator than they naturally would lie. The effect is miniscle, but it is there...
OH dear, does that mean that perhaps in some future I will not have any birthday at all? It's hard enough only having one every fourth year, if they remove those seconds surely the Feburary the 29th must be their next target!
Assuming you said that because you hate Bush, bad plan. Time is your friend. If Nov 2004 was, say, tommorow, Bush would win by a landslide. Time is your friend. If anything, you need to push it back.
So is Syria hiding Saddam, or just his buddies?
This slowing has got to be caused by tall buildings, as we are taking mass that once was in underground and placing it high above the ground. I don't remember what this is called, but there's some nifty name for it. We're also doing the same thing with fossil fuels, just burning them inbetween! :-)
Considering the Aztec calender was much more accurate then ours is today, why not just use that for our day-to-day lives?
The bad news: The Earth with end Dec 12 2013. =)
"The price good men pay for indifference to public affairs is to be ruled by evil men." ~Plato (427-347 BC)
... network security? Suppose that you are trying to track some asshat mail-harvesting bot and you are collating a bunch of server logs from different systems to do it. It is helpful for those server logs to have timestamps on them, and it's helpful for those timestamps to have very little skew between their respective clocks. If some people are putting in leap seconds correctly, and some aren't, that could make a difference in how easy your Perl script can correlate the data.
instead of decimalizing the length of the day (which has struck me as a supremely silly idea, because the day length changes, and the year is not an integer multiple of the day anyway), why not give up on the solar cycle altogether and count everything in terms of seconds since 1970?
In space we could define a "day" as being ten kiloseconds long, or about 27ish hours. A kilosecond is a good unit of time, about two and two-thirds hours. A megasecond is also a good unit of time: about three of them to a month. Ten megaseconds, also good, it's about the length of a season. Keeping track of the date that way is pretty intuitive, too; right now it's 1050.7Msec since 1970. Easy number to keep track of; at least no harder than the year.
Sucks for scheduling, though.
We could do a whole lot worse, and it'd have some advantages as well as the big disadvantage of not corresponding to the calendar date. It'd be most useful when we've got to deal with space-based calendars, or other planets' cycles. Or something.
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
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.
I don't know the meaning of the word 'don't' - J
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 the way, US territory in general is a good place to clean up - the most weapons of mass destructios are there.
"I shall explain this by waving my hands about in an appropriate manner." -- Cambridge University Math Dept.
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.
For all intensive purposes, "whom" is no longer a word. That begs the question, "who cares"?
Well, if Velikovsky was correct, we might not have to worry about it in 60,000 years. Since Venus swings by us and messes things up on a much shorter time period.
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.
autopr0n is like, down and stuff.
By your logic, using 6.2830 divisions would be a terrible idea.
autopr0n is like, down and stuff.
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.
GCHQ Quantum Insert installed. If only our tongues were made of glass, how much more careful we would be when we speak
You do realize the chance of having the earth orbit the sun at exactly 365.0000 days is highly unlikely.a That's to perfect a number...
Hmmm... Pie...
This is about keeping our computing time very close to the physical earth rotation of the earth.
Since 1970 we have had 26 leap seconds.
But does it really matter if the sun is at zenith at Greenwitch at 12.00:00, or a half a minute after?
Isn't it at lot more important for all systems to correctly identify if a binding financial transaction made with a digital signature was made before or after the signature was revoked?
All these leap seconds are just corrections for earth rotation, and are a source of time calculation errors in software systems.
> 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.
I think their idea is that if the rotation period *gradually* shortens
Sorry, I meant "orbit period", not rotation.
Table-ized A.I.
"Leap seconds are an evil Zionist plot to cover up the fact that these filthy dogs want to stop the earth so that only America has sun so that they can grow all the food and sell it to Arabs at a hefty markup because they are jealous of Arab oil. Sadam will expose these filthy toads and put the Earth back to the way our Great Allah intended."
Table-ized A.I.
We missed our chance to do that. Now we will have to wait until y3k so that we can implement the new policy. Only 997 years to go, so get ready!
No, I don't trust in god. He'll have to pay up front, like everybody else.
is going to grind to a halt, i hope i end sunny side up.
I know you are psychotic, but please make an effort.
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.
The Earth has gotten fat. If we can get it to suck in, it'll sping faster! Think: ice skater raising her arms in the air as she spins.
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
watch this
No! If they get rid of leap seconds, that'll cut my sex time in half!
Leap seconds are fundamentally different from time zones and daylight savings time because they cannot be precalculated*. Leap seconds occur when the International Earth Rotation Service (IERS) has actually detected a change in the earth's rotation meriting a leap second, so in a fashion they only occur after the fact. Besides, it's somewhat counterintuitive to say that minutes have 61 seconds, when occasionally they do.
There are other issues to deal with, too, such as times before the epoch (read: before our current time systems), POSIX's brokenness, maintaining the monotonicity of time, etc. Time is a lot harder to deal with than most people realize.
* DST can also be changed, but it at least remains the same from year to year unless changed.
Imagine a large country..say the US.
Ok, let's say around 6 and a half trillion in debt is accruing intrest, and they're paying.
How much is that leap second worth to the debtor?
How much for the creditor?
Now imagine slacker code monkey omits leap second calculation, chaos breaks out cats and dogs...you get the idea.
I'm not exactly sure, but I bet they compute interest to the second on amounts like that and round down payouts on the bonds, three-quarters of a penny is hard to deposit, but I bet it's counted. I want a red swingline stapler all of a sudden.
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...
I have no problem with your religion until you decide it's reason to deprive others of the truth.
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...
I have no problem with your religion until you decide it's reason to deprive others of the truth.
Is France a member?
Do they take requests? ("I'd like an extra long sunset this Friday night... I have a date!")
We need to speed up the Earth's rotation! Problem solved!
~CGameProgrammer( );
Oops. That is what I meant.
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.
.9 seconds of cosmic time.
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
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.
Darthtuttle
Thought Architect
After a quick browse through the replies, I didn't see this mentioned -
If UTC is allowed to become out of sync with 'normal time', how do you calculate UTC on your PC? At the minute, its quite simple - its the number of seconds since 00:00 01/01/70. Easy.
If you no longer have leap seconds, UTC goes out of sync with the PCs clock - we would need to have software updates an OS patches to account for any gained leap seconds, and the point in time at which they occur(ed).
If I talk about a time in the future - how do I convert it from UTC to 'normal' time?
Of course I could have missed the point here, and leap seconds could be added to 'normal' time at regular intervals (there by making the calculation easy), but what if they are not?
Steve.
Well, if the Earth is slowing down, isn't that a problem? Someone should immediately address this issue!!!
A few years back I had to work 12 hr shifts for awhile, when our new systems went production. As the maytag SA, I spent quite a bit of time reading a book by the US Navy that contains the supporting information for the US Navy Nautical Almanac.
Contained were much time related information including that TAI is (was) and average of about 300
cesium clocks and some fewer hydrogen ones. The thing that dropped my jaw was the revalation that in secrecy these clocks were steered by the commitee with some small infrequent tweeks.
The ThermoDynamic Police are concerned that leap seconds create time where none existed before.
We are investigating this as a possible attempted violation of the laws.
Paul Steele
Thermodynamic Police
Legum non sanximus eam tantum exsequimus!
We don't make the laws we just enforce them!
The second is a base unit for a whole shitload of derived units. It would screw up Mhz measurements, energy measurements, physical constants and no end of other hell. It would also make using data sets that extend over large periods of time hell. Furthermore, the oscillations and perturbations of this planet have no relavence at all off this planet. This means the software in those probes and satellites we put up instantly become wrong. There is nothing in the least elegant about any of this.
I'm pretty sure that the question of whether "celestial time" and "atomic time" are the same has been thought about, and even if there aren't any direct tests of this, I think there have been plenty of indirect tests. The best off-the-cuff theoretical reason I can think of for the equivalence is relativity. We have astronomical tests of relativity (red/blue-shift effects, if nothing else) and microscopic tests. There are even a few that combine the two, like the famous atomic clocks in an airplane and on Earth. The theory works in all circumstances and I think that if the times weren't the same, you could violate the equivalence principle (measure the same duration celestial time and atomic time; if the two are different, you know you're in a gravity field).
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!
If anything, I suggest we use your idea to slow down earth by an extra hour per day or so...
Let's have a poll: How long, do slashdot readers think, would the perfect day be? I'd vote for 26 hours.
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.
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".
So, if I ever go to UoT, I'll refrain from asking around what time it is. I wouldn't understand.
__
Men with no respect for life must never be allowed to control the ultimate instruments of death.
GW Bu
365.2425 days. So our speed decreased. This would also cause our orbit to change, Twilight Zone style!
You can't judge a book by the way it wears its hair.
oh shit, does this mean we need to launch a vessel into the center of the earth and set-off a few nuclear explosions??
my karma will be here long after I'm gone
Use Julian dates if you want a decimal time. Astronomers have been using this for a long, long time... Noon on Jan 1 , 2000 is Julian date 2451545.0. Use this number to convert your time to a Julain date. BTW, Julian days switch from one day to the next on noon rather than midnight because astonomers tend to work nights :)
There are 10 types of people in this world, those who can count in binary and those who can't.
A lot of current mars missions tell time by what Mars longitude the Sun is over. If you know the longitude where your rover or lander is, a simple subtraction tells you how high the sun is in the sky. No need for leap seconds as the clock is directly tied to the Sun's position.
There are 10 types of people in this world, those who can count in binary and those who can't.
The problem with leap seconds is that they are not predictable. You can work out some future event in TAI, but you cannot convert it to UTC because you don't know when the next leap second will happen.
If you work in UTC to plan something in the future (say a space mission 4-10 years from now) you can suddenly find all of your schedule off by a second (or more) when a leap second is added or subtracted.
Of course, everything is usually tied to the wall clock which is tied to UTC an not TAI... so there's always a danger that a schedule laid out before a leap second is added can be off... and being off by a second is a big deal in a space mission when you're going several kilometers per second.
I say scrap leap seconds until someone can come up with a reliable model of the Earth's rotation so that leap seconds can be predicted instead of being random. When accuracy to the second matters, who the hell wants a random offset on their clock?
There are 10 types of people in this world, those who can count in binary and those who can't.
The same thing would happen with any other angular mesurement system, since any rational fraction of a full would have an irrational answer for sign and cosine (other then 180/90/0 degrees) IIRC.
autopr0n is like, down and stuff.
so let me get this straight - for centuries, we've had systems of time that we've bent around the rise and set of the sun. they've all pretty much sucked. we like to think we're getting better at it. - ok. NOW we have a situation in which we have utilized our latest temporal system (no judgements being made on it's accuracy) in order to calculate the precise speed of rotation of the globe on which we live. our conclusion: the earth is slowing down! um, isn't there just the *slightest* possibility that our time system just doesn't fit the day/night cycle correctly? especially when we're throwing seconds into and out of said system in order to make it work? seems kinda like last week's article on a superconducting diamond, where the guy said that "if it's not a superconductor, it's violating the 2nd law of thermodynamics" (not allowing that he may have fu#$ed up)
but what the hell do I know, I was a jazz major, we bend time just to play music . . .
I grow impatient with the international community. We know they are hiding these leap seconds. They have thumbed their noses at us for too long. We have a clear mandate to inititate a time change. We will go in with our coalition for free time and find these missing seconds with whatever force is necessary. These timekeepers have the power to prevent this. All they need to do is surrender the leap seconds and submit to our inspections of their timekeeping devices. But we are not infinitely patient. Their time is running out.
If Slashdot were chemistry it would look like this:Cadaverine
it seems everything French starts off well but is never really completed
Like french kissing? Somehow there's always a headache, or a phone ringing, or something else before it gets where you wanna go.
Or maybe that's just me...