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US DoD Poll On Leap Seconds
@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."
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)
Admit it. You post strawman arguments as AC so you get modded Insightful for refuting them, rather than Troll
No there isn't, but you can make it culminate at noon.
rj
I'd be more interested in killing Daylight Savings Time than dealing with Leap Year.
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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.
Engineering is the art of compromise.
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.
We don't need even one more second of Bush presidency. :)
Keeping leap seconds synced is pretty important across comms networks.
Engineering is the art of compromise.
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.
If you're going to do this sort of thing - adding seconds to the clock here or there - it shouldn't be decided upon by some review committee. There should be a planned algorithm that kicks in, and the simplest one that actually does the job should be used. The bottom line is that a watch should be able to do it. If you do this, you're able to program devices to account for leap seconds instead of having to manually put in fudges which is an error prone process. You also get the possibility of adding leap milli-seconds or micro-seconds so fine grained adjustments are possible where required, whereas it would be much harder (though not impossible) to do that if you're manually correcting.
It cannot be done. Leap seconds are dependent on unpredictable, chaotic natural events -- namely the fact that one day in not exactly 24 hours in length. The daily error is not constant, so the only way to determine when a leap second is required is through astronomical observations.
> 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.
Warning: this article may contain humor, sarcasm, parody, and perhaps even irony. Read at your own risk.
and if anyone doesn't like leap seconds, all they have to do is use one of the time scales which don't use them, like TAI.
It's exceedingly silly and stupid for people to keep trying to change UTC 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.
"National Security is the chief cause of national insecurity." - Celine's First Law
Changing the length of a second will end up changing almost everything in our lives. It would be an enormous undertaking, redefining, among many other things, electromagnetic wavelengths and the speed of light. Speed limits would change, computers would have to handle travel time calculations differently, and the length of the workday would change slightly.
It was hard enough to get the world to change to the metric system (with notable holdouts still remaining). Changing the very definition of one of the six core SI units would be nearly impossible.
You can never go home again... but I guess you can shop there.
Let's just remove the problem entirely!
I suggest... the French Republican calendar.
And a good Tridi, 23 Fructidor, Year 216 to you too.
Why don't we just get Superman to fly around the Earth really fast to slightly change its rotation. If he can reverse time, surely he could adjust it sightly so that everything would work out.
I don't understand what the DoD has to do with time, standards or measurements.
Is the DoD trying to say now Muhahaha! Now we control time itself, submit all ye to "civilian time"?
We need to get the opinion of an expert, not some random poll.. perhaps the DoD should seek the advice of the master of timecube theory Dr. Gene Ray.
Bringing liberty to the masses. - http://freetalklive.com/
I think that says more about make than it says about timekeeping.
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.
thegodmovie.com - watch it
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.
upon the advice of my lawyer, i have no sig at this time
No they don't. If you'll look at the chart in the Wikipedia article, 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.
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What significance does this have for people who live in their parents' basement?
Have gnu, will travel.
... 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.
> We currently cannot predict those variations, and as such, the leap seconds are
> determined based on astronomical observation and applied as needed.
I know that, but zoneinfo has to be updated frequently anyway to accomodate the whims of princes.
Warning: this article may contain humor, sarcasm, parody, and perhaps even irony. Read at your own risk.
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.
That's cuz our times are valuable, unlike yours, you third-world poor trash!!! Go recycle copper and stuff.
Fuck systemd. Fuck Redhat. Fuck Soylent, too. Wait, scratch the last one.
We rotate the same way we orbit, so the Earth rotates (from the point of view of the distant stars - the sidereal day) one more time in a year (366.24) than the number of solar days (365.24) - the number of times the sun circuts the sky. The length of the sidereal day is 23:56:04.1 long, and the solar day is 24:00:00 (roughly!). That extra 4 minutes is the Earth rotating 'a little extra' to put the sun in the same place in the sky since it's moved around it a little since the last noon.
If you have ever tried the coin rotation trick, that might help you out visualizing it. Glue one coin to a piece of paper with the 'head' up. Align another coin above the first, with the head also up. Now, rotate the second coin around the first, keeping the edges in contact (no slipping). How many times does the second coin rotate?
Most people will guess once, because the circumferences of the coins are the same. However, because the second coin 'orbits' the first as well as rotating on its own axis, it actually rotates TWICE. In our simplified coin scenario, there are 2 sidereal days, but only one solar day in a year. Look at how many times the bottom of the rotating coin 'sees a noon', and you'll be convinced.
http://en.wikipedia.org/wiki/Circadian_rhythm#The_myth_of_the_25-hour_day
Sam ty sig.
No, they don't. The Earth's rotation rate is slowing due to tidal friction (and slowly pushing the moon away in the process, since angular momentum doesn't just vanish). The SI second was set based off of the average solar day back in the 1700's or so, and the Earth's average rotational period has slowed measurably since then. We have only added leap seconds, never subtracted them, and likely never will, despite a significant variation in the rate of slowing.
The problem is that we want to measure different periodic processes via the same unit - the second. The second was originally based off of the average length of the solar day, but then was redefined in terms of atomic standards. The average solar day, according to atomic standards, has been lengthening somewhat erratically. Either we give up using the second as a fundamental unit in the SI system, suitable for meausring times vast and small, or we give up having our clocks based on the second but choose some other 'variable' unit, synced to the sun (such as UT1 time), or we compromise and stick a leap second in from time to time to assure that UTC and UT1 remain within a second of each other - which is what is currently done. There really isn't an easy way out since the periodic processes of nature that matter to us are not neatly in ratios. Do we really want a 'science' time, and a 'civilian' time?
As you say, one day, programmers will wrap these difficulties up in libraries nicely and neatly so that it just 'works', but it will be based on an arbitrary table of leap seconds, much like we have an arbitrary table of time zone rules in our zoneinfo files. Part of the problem was due to the POSIX standard for time NOT being done properly. UTC actually specifies that the 'extra' second means that there are 61 seconds in a particular minute - i.e. 23:59:60 is a valid UTC time when a leap second is inserted. Unfortunately, POSIX time 'repeats' a second instead. POSIX time goes.... 23:59:57....23:59:58.... 23:59:59.....(zip! leap second!) 23:59:59.... 00:00:00.... 00:00:01... etc.
There are some complex tradeoffs associated with this. It simplifies the numerical calculation of traslating POSIX time (since POSIX time really is represented as the integer number of seconds since 1970-Jan-01 00:00:00, and the leap seconds are ignored) to 'clockface' time (i.e. The year, month, date, hour, minute and second). On the other hand, it yields incorrect answers when two POSIX times are naively subtracted to figure out the time delta between the time marks; one has to modify the 'obvious' subtraction algorithm with a somewhat complex lookup table procedure to get an accurate delta. UTC is more complex because the occassional 61 second minute requires that you consult a lookup table to translate UTC seconds to year-month-date-hour-minute-second form, but subtraction easily yields the correct delta between the time marks. If we want to stick with SI seconds and schedule ourselves with the sun, there will always be some messiness!
I think the US should have one time zone, and it should be based on NYC time. -5/-4 UTC for everybody! Who cares if California would have the sunset at 2230 today?
Fine by me, and I'm a native Californian.
There's no rule that says business hours need to be 9 to 5. Since you already have to convert what "time" it is in a faraway place you're calling, it's not a big deal. In San Francisco, I can't make any calls after 1pm to East Coast offices and expect to get anything done. What the clocks say over there doesn't really matter. For all intents and purposes, New York business hours are 6am to 2pm from my perspective.
I'd be content for the entire planet to move past the idea of time zones entirely. It's an outdated idea from a time when you needed physical references to the passing of time, and when it didn't matter that the times didn't line up in faraway places. Just think of all the things it would simplify: flight arrivals/departures, conference calls, news stories--and it would make am/pm an unnecessary distinction, too. 0514 would really be 0514. Everywhere. I'm okay with "business hours" for me being, say 0100 to 0900, and 2200 to 0600 in some other place. They're just numbers.
Tradition and conditioning, however, are unbeatable--and the idea of "noon" being the middle of the day has undeniable intuitive appeal (even if it's rarely accurate).