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."

Comments

Re:Are leap seconds really all that important?

[Anonymous Coward]

Compare absolute time vs relative time vs elapsed time vs hammer time...

Kill DST instead!!!!

[wealthychef]

I'd be more interested in killing Daylight Savings Time than dealing with Leap Year.

Re:Kill DST instead!!!!

[Kjella]

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.

Leap seconds fix a diferent problem

[EmbeddedJanitor]

Leap days correct our orbit around the sun to keep December/January in the middle of winter for the Northern Hemisphere.

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.

Re:Leap seconds fix a diferent problem

[Dannkape]

According to wikipedia, there seems to have been 24 leap seconds in the last 36 years. For solar noon to move a single hour away would take over 5 millenia.

Of course, they do give the news something harmless to report on every once in a while...

Re:You and me both!

[Anonymous Coward]

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.

Re:Automated and consistent leap seconds

[klapaucjusz]

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.

Re:Are leap seconds really all that important?

[xstonedogx]

I dunno. When it's Miller Time all those other times kinda look alike.

Re:You and me both!

[BitterOldGUy]

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!

Re:You and me both!

[techno-vampire]

Cats have servants.

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.)

Re:Automated and consistent leap seconds

[techno-vampire]

More to the point, it appears to average out, so we could be inserting them just to have to remove them a decade later.

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.

Re:Slightly OT: Earth Rotations?

[jeepien]

... 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.

Re:Automated and consistent leap seconds

[__aajfby9338]

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.