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US DoD Poll On Leap Seconds
Posted by
kdawson
on Mon Sep 08, 2008 06:59 PM
from the great-leap-forward dept.
from the great-leap-forward dept.
@10u8 writes "For time scales to leap, or not to leap, has been the question here before. The ITU-R will be considering leap seconds again in a few weeks. This week the USNO posted a survey about leap seconds by the US DoD. The issue has civil implications as well as technical ones, and there is a demonstrated way to respect the history, remove leaps from navigation and POSIX time, yet keep the sun overhead at noon."
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[+]
The Future of Leap Seconds 429 comments
@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."
[+]
U.S. Moves to Kill Leap Seconds 601 comments
blacklite001 writes "Not content with merely extending Daylight Savings Time, the U.S. government now also proposes to eliminate leap seconds, according to a Wall Street Journal story. Their proposal, 'made secretly to a United Nations body,' includes adding 'a "leap hour" every 500 to 600 years.'
Hey, anyone remember the last bunch of people to mess with the calendar?"
[+]
Vote To Eliminate Leap Seconds 531 comments
Mortimer.CA writes "As discussed on Slashdot previously, there is a proposal to remove leap seconds from UTC (nee 'Greenwich' time). It will be put to a vote to ITU member states during 2008, and if 70% agree, the leap second will be eliminated by 2013. There is some debate as to whether this change is a good or bad idea. The proposal calls for a 'leap-hour' in about 600 years, which nobody seems to believe is a good idea. One philosophical point opponents make is that the 'official' time on Earth should match the time of the sun and heavens."
[+]
News: Leap Second To Be Added Dec 31, 2008 255 comments
ammorris writes "Don't be the laughingstock of your friends when you shout 'Happy New Years' a second too early ... The International Earth Rotation and Reference Systems Service has announced that a leap second will be added on December 31, 2008 at 23h 59m 60s, meaning that this year will be exactly one second longer. The last leap second occurred Dec 31, 2005; they are added due to fluctuations in the rotational speed of the earth. You can read all about leap seconds on Wikipedia."
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Are leap seconds really all that important? (Score:5, Insightful)
I thought we had leap years to take care of the discrepancy between our calendar and the actual orbit around the sun. Would a leap second even be made longer by any noticeable amount? What about sporting events? Someone who misses out on a world record by a tiny bit would complain that the record h older had more leap seconds in his race! (Okay, that one was a joke, but the rest I'm serious about)
Re:Are leap seconds really all that important? (Score:5, Funny)
Compare absolute time vs relative time vs elapsed time vs hammer time...
Parent
Re:Are leap seconds really all that important? (Score:5, Funny)
I dunno. When it's Miller Time all those other times kinda look alike.
Parent
Leap seconds fix a diferent problem (Score:5, Informative)
Leap seconds correct for the rotation of the earth to keep the sun above at noon.
If we dispense with leap seconds then this relationship will slowly change and noon will eventually be dark.
Parent
Yep... (Score:5, Insightful)
It's exceedingly silly and stupid for people to keep trying to change UTC [wikipedia.org] so it doesn't track solar time. That what it was intended to do. If you made the wrong choice, live with it, or change time scales. If it's being forced on you, quityerbitchin', and convince whoever decided on UTC to change. Stop trying to turn UTC into something it isn't, there are other people out there who made an intelligent decision, and depend on it's characteristics.
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Re:Leap seconds fix a diferent problem (Score:5, Informative)
Of course, they do give the news something harmless to report on every once in a while...
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Re:Leap seconds fix a diferent problem (Score:5, Funny)
If we dispense with leap seconds then this relationship will slowly change and noon will eventually be dark.
In that case, we rename "noon" to "midnight", and "midnight" to "noon"
then "AM" can mean "After-Meridian" and "PM" can mean "Pre-Meridian"
I thought of everything. Problem solved forever.
Parent
Re:Or played with GPS etc (Score:5, Informative)
That's correct, because correcting the epoch for leap seconds would cause glitches in positioning as the corrections were applied. Instead, GPS broadcasts a UTC correction so the receiver can convert to UTC if required: ahref=http://www.navcen.uscg.gov/pubs/gps/sigspec/gpssps1.pdfrel=url2html-16574 [slashdot.org]http://www.navcen.uscg.gov/pubs/gps/sigspec/gpssps1.pdf>
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Re:Slightly OT: Earth Rotations? (Score:5, Funny)
... does anyone know if the rotation of the earth around the sun mean that we actually rotate 366.25 times per revolution, or 364.25?
Yes, of course someone does.
Parent
Not quite (Score:5, Informative)
No there isn't, but you can make it culminate at noon.
rj
Kill DST instead!!!! (Score:5, Insightful)
You and me both! (Score:5, Funny)
I'd be more interested in killing Daylight Savings Time than dealing with Leap Year.
My cat wakes me up in the morning. She doesn't adjust. Because of her, I'm a morning person. Unfortunately, 90% of society are night people. Meaning, any social activity is past my bedtime and I become a wet blanket because I start yawning at everything at 20:00.
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Re:You and me both! (Score:5, Funny)
I think your REAL problems are as follows:
You have a cat.
Your cat controls you.
You characterize and categorize people (90%, society, night people) in terms of what they can give you (social activity).
You speak in military (24 hour) time unnecessarily.
You admit your own faults, but rather than fix them, you prefer to revel in your own meekness.
Parent
Re:You and me both! (Score:5, Funny)
I think your REAL problems are as follows:
You have a cat.
Your cat controls you.
You characterize and categorize people (90%, society, night people) in terms of what they can give you (social activity).
You speak in military (24 hour) time unnecessarily.
You admit your own faults, but rather than fix them, you prefer to revel in your own meekness.
Dogs have masters.
Cats have servants.
I recognize my overlord and serve her. And as a result, my life is filled with a wondrous furry glory!
The Egyptians worshiped cats as gods and the cats have never forgotten that.
Military time is also computer server time. And if you deal with computers across at least one time zone you may want to use Zulu time too. Oooooo, I used another military term. You know why!? Because, I serve in the army of cats!
Parent
Re:You and me both! (Score:5, Funny)
I, for one, welcome our feline overlords. (I'd better, I have one watching me type this, ready to sink his claws into my leg if I type the wrong thing.)
Parent
Re:Kill DST instead!!!! (Score:5, Insightful)
Killing it? I want to change them completely, and wintertime too. Now, I live a bit further north than most people (60 degrees latitude) and what happens in the winter is that I, like most people, head to work in the dark and come home in the dark. Maybe you get to see some sun on your lunch break, but unless you got an office with a view you won't see much of it otherwise. If we have like 6 hours of sun, they should be 4PM-10PM so you can do some outdoor activity after work. What happens now is I sit indoors during the day because of work, and I sit indoors in the evenings because it's dark and cold outside. I haven't got any stats to back it up but I'd think most people work indoors these days, the reason to have light == noon so you could run around outside just isn't there. I'd be happy with mornings that suck (some more) and evenings that were bright and nice all year round.
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Re:Kill DST instead!!!! (Score:5, Funny)
Parent
I know! (Score:5, Funny)
Let's just remove the problem entirely!
I suggest... the French Republican calendar.
And a good Tridi, 23 Fructidor, Year 216 to you too.
Re:Automated and consistent leap seconds (Score:5, Insightful)
There should be a planned algorithm that kicks in,
This assumes that we know when, in the future, we'll need to insert leap seconds. And we don't.
Leap seconds are introduced in order to compensate for medium-term variations in the earth's rotation speed. We don't have a good understanding of the way the earth rotates -- knowing what UTC time it will be in ten years' time is about as difficult as predicting the weather for next week-end.
Parent
Re:Automated and consistent leap seconds (Score:5, Informative)
No they don't. If you'll look at the chart in the Wikipedia article, [wikipedia.org] you'll see that since they started using them in 1972, they've never had to subtract a second. Either no change, or +1 second.
Parent
Re:Automated and consistent leap seconds (Score:5, Informative)
> There should be a planned algorithm that kicks in, and the simplest one that actually
> does the job should be used.
There is none. The rate of rotation of the Earth is slightly irregular in a not entirely predictable way.
> I don't think I even own a time keep device where this level of accuracy matters.
> Perhaps my GPS?
Definitely your GPS. It cares about nanoseconds.
Parent
Re:Automated and consistent leap seconds (Score:5, Informative)
Definitely your GPS. It cares about nanoseconds.
But so long as all the satellites are in sync with their atomic clocks showing the same time, does it matter??? Even without them being in sync, doesn't the GPS use time and rough location to locate the satellites (unitil it's logged on) and then isn't it the round trip time taken by signal that's being measured? Is there any dependancy on leap seconds?
GPS doesn't use UTC for its measurements; it uses its own system of GPS time for its measurements, and then calculates UTC using a correction value transmitted by the satellites in order to be able to display UTC (or any other UTC-derived time) for the user.
Also, it doesn't "log in" in any usual sense, as the communication is purely one-way, from the satellite broadcasts to the receiver. Thus, it also doesn't measure round trip time, because there is no round trip. What it does is to receive the signals from multiple satellites, each of which essentially transmits a signal saying "I'm satellite number A, my location is B, and the time is C", and then solve a system of equations to figure out what time it was when it received the signals from each satellite, and thus how long each one-way trip took. Then it can do the geometry to figure out where it must be. The actual mechanism of accomplishing this is a whole lot more complicated, but on a very simple level, that's what's being done.
The reason it takes at least four visible satellites to produce a 3D fix is because it needs to solve a system of at least four equations with four unknowns: X, Y and Z spatial coordinates, and time. More than four satellites are normally needed for good accuracy, since the each measurement is usually a lot more noisy and less precise than is desired. Additional measurements let the receiver do more math to try and filter out the noise.
Parent
Re:Why not just change time pieces to include the (Score:5, Informative)
That's exactly the point. Changing software in military or even space systems isn't exactly trivial, maybe not even possible, plus you need a method to constantly provide (UT1-UTC) to the systems that rely on UT1 (astronomical time) being equal to UTC by less than a second. Like the radio controlled clock in your home. Or the time signal transmitters would have to be redefined not to transmit UTC but some new time scale, which would be a mess for GPS.
UTC without leap seconds is basically TAI (international atomic time) - a strictly linear SI second timescale as precise as we can reproduce it.
Just distribute (TAI-UTC) and (UT1-UTC) together with the usual time signals, leave UTC alone (with leap seconds) and you're all set and can use what you need. There is no one time scale; Einstein told us so. Better accept it.
Parent
Re:Why not just change time pieces to include the (Score:5, Informative)
The problem being, the need for a leap second is not predefinable, unlike a leap day. Leap seconds are needed to compensate for slight (millisecond range) variations in the length of each day, due to the earth's rotation speed not being constant. We currently cannot predict those variations, and as such, the leap seconds are determined based on astronomical observation and applied as needed.
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Re:Why is this the DoD's responsibility? (Score:5, Informative)
Navigation depends on time. The Navy is very interested in navigation. That's why they established the Naval Observatory [navy.mil] in 1830.
USNO employs some of the formost experts on the subject. They are soliciting the opinions of some of the other stakeholders.
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