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)
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.
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.
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?
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."
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;
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
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?
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?
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...
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
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"?
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