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If we don't bother with leap seconds, then the distance that the sun will be off from being directly overhead at the equinox is about the same as it is now from being a couple of hundred miles away from the meridian. A simpler solution to the problem would be to, every couple of thousand years, have a one-hour reset.

Actually, the problem is worse than that (and shows the futility of the leap second system), because the earth is of course slowing down.

So, while we now have to add a leap second every few years or whatever, eventually that will become every year, then two every year, and then the current system will break, because right now we're only allowed two leap seconds per year by the current standard.

At best, adding up to two leap seconds per year will be able to keep up with the slowing earth for about another 200 years. If we added no leap seconds for the next 200 years, however, we'd only be off by maybe 5 minutes or so.

So, the current system simply can't work for very long anyway. It's going to break well before we'd have gotten anywhere close to a need for a "one-hour reset."

The ITU-R first received this issue as Question 236/7 in year 2001. They have spent nearly 15 years coming up with this list of 6 methods for dealing with leap seconds. In that note the most recent "Method D" from a group of countries who prefer no change because they are not satisfied with the documents that have been submitted to the ITU-R during the past decade.

The debate continues because it is not a technical issue. We know how to count SI seconds by physicists watching cesium atoms, and we know how to count calendar days by astronomers watching the earth rotate. The question is about time producers and time consumers -- which of the time producers will have the hegemony, and whether the time consumers have enough agency to choose what time scale to use for their applications. The question is whether the days of the civil calendar will remain related to the rotating earth, or change to be 794 243 384 928 000 hyperfine oscillations of cesium-133.

The divergence is (roughly) quadratic; those estimates (well, for leap "something > 1 second") are off.

UTC is designed so that the sun will always be up during the day and down at night.

There have been 25 leap seconds since 1972. At that rate, it will take around 6000 years for UTC to be even an hour different from TAI.

The long term behavior is a quadratic, so it will speed up; there could easily be multiple leap seconds per year by 2100. Likewise, the difference was about 4 hours only 2000 years ago (and, yes, we do have usable astronomical data going back to about 800 BC).

UTC is designed so that the sun will always be up during the day and down at night.

There have been 25 leap seconds since 1972. At that rate, it will take around 6000 years for UTC to be even an hour different from TAI.

The long term behavior is a quadratic, so it will speed up; there could easily be multiple leap seconds per year by 2100. Likewise, the difference was about 4 hours only 2000 years ago (and, yes, we do have usable astronomical data going back to about 800 BC).

one of the links from that page talks about how using custom timezone files you can use non-leap seconds and still translate to accurate real-world values. I'm not terribly familiar with time keeping protocols; installing ntp and pointing it at a server is about as far as I can manage. Do you see a problem with the approach laid out at "Correct precision handling of leap seconds using code already on POSIX systems "?

A problem for sysadmins is that the status quo of the standards requires that we choose which standard we want to violate. We can violate the specification of UTC by not counting 23:59:60 or we can violate POSIX by counting it or we can violate POSIX and the SI second by not actually keeping the system clock on UTC using smeared seconds that are not suitable for tracking projectiles and other real-time applications. This problem is old, 50 years old, as seen in the 3 plots on this web page.

Look deeper at one of the underlying problems in this issue -- see blockquote in the "UTC in 1982" entry here. That paragraph was written by one of the folks who actually worked in the field of timekeeping, and those are the folks who produced the documents that get approved by the votes. (All the votes by those agencies that make the official documents are done by delegates who know next to nothing about the subject matter.) See how that 1982 paragraph crows about the way that UTC with leap seconds has solved all problems and become accepted by everyone. They were oblivious to the problems that would crop up. The process of making the decisions and producing these international recommendations has not changed much in the subsequent 30 years.

missing link

If they tried being more accurate they'd have to explain what time scale they were broadcasting way back then.

My God, it's full of words!

If they tried being more accurate they'd have to explain what time scale they were broadcasting way back then.

There is no trademark or copyright for book titles. Period. Ever. In the US.

Then explain Wiley's FOR DUMMIES mark and what its owners have done.

anything that runs its kernel on GPS time can give correct UTC time by following this prescription http://www.ucolick.org/~sla/leapsecs/right+gps.html

Perchance something like this example worked with existing deployed and tested code? http://www.ucolick.org/~sla/leapsecs/right+gps.html

The time service bureaus used to insert leap milliseconds at almost any time. See the bottom plot at http://www.ucolick.org/~sla/leapsecs/amsci.html where there were 29 leaps in 3 years.

The situation can be explained in three pictures.

Using already-deployed code, here is one way to solve the problems.

The situation can be explained in three pictures.

Using already-deployed code, here is one way to solve the problems.

And while 20 light years might be small by astronomical standards, human beings haven't even been two light *seconds* away from the earth.

FWIW, Voyager 1 is about 14-15 light-hours away now.

Something to consider, though - not all radiation is the evil, hazardous, cancer-causing flesh-melting variety. Light is radiation, which is, well what they'd been using to study this thing. The shallow end of the details pool can be had here(pdf).

Also, they're not just blindly poking around at random bits of cubic space - they're starting with stars, eh?

The submitter should have included this bad boy (PDF) in his linkage. Expecting to see methodology on a discovery.com website? You'll have an easier time getting Steve Ballmer to cough up the source code for MS Office.

PS: As an EE, you should know the specific type of magic: It's most commonly referred to as FM.

the deviation is quadratic, so an hour accumulates 800 to 900 years

the deviation is quadratic, so an hour accumulates 800 to 900 years

The reason we adjust for solar time is that two standing international agreements demand that we define the day as a "mean solar day". Computer people and farmers can use different times if mean solar days are not made illegal and replaced with atomic days, that's what zoneinfo is for.

The reason we adjust for solar time is that two standing international agreements demand that we define the day as a "mean solar day". Computer people and farmers can use different times if mean solar days are not made illegal and replaced with atomic days, that's what zoneinfo is for.

The historical record of time_t is already ambiguous and cannot be corrected by abandoning leap seconds. There is a way to get leap seconds out of the kernel and into user space which amounts to reclassifying them as decrees of change of civil time and putting them into zoneinfo while letting the broadcast time scale not have leaps. It's a matter for posterity whether the word "day" will be re-defined by the ITU-R, changed from the current treaty-specified "mean solar day" to a technically-defined "atomic day".

The historical record of time_t is already ambiguous and cannot be corrected by abandoning leap seconds. There is a way to get leap seconds out of the kernel and into user space which amounts to reclassifying them as decrees of change of civil time and putting them into zoneinfo while letting the broadcast time scale not have leaps. It's a matter for posterity whether the word "day" will be re-defined by the ITU-R, changed from the current treaty-specified "mean solar day" to a technically-defined "atomic day".

a billion years ain't that long if you're a planet...

Yes, it is. Our sun's lifespan is about 10 billion years, and it's half-way through. In other word, the solar system should be having its mid-life crisis now.

You don't need to know Morris code any more, but you do need to study up on radio & electronic theory. Radio shack used to sell the Ham license study guides, but I don't know if they have them any more.

Morris code, would that be the way that Morris Dancers signal each other?

Until 2007 legal time in the US was mean solar time, and that has no leaps, so this is the first leap second for the legal US time. Officially, of course, USNO and NIST were keeping UTC, but that didn't make it legal. The difference shows up in computer time scales.

The universe likely has neutral charge. Also see a more detailed discussion on the subject.

you can't really measure anything going on inside it.

reference here (2nd answer)

I know an engineer working on this project who jokes that "Thirty Meter Telescope" is a good name because if funding is cut they can downscope to the "Twenty Meter Telescope" without having to change any of the "TMT" logos.

Could someone please copy and paste the contents of TFA. It's in a proprietary file format and Stallman has forbidden me from opening it.

Sounds like sudo/gksudo or super (which attempts eliminate some of the insecurities of sudo by only allowing specific commands to be run -- not that this can't be done with sudo).

Pair creation supernovae were predicted decades ago. The conditions for their formation are a bit strict and they do not appear to be very common at this point. Black hole creation is probably must more common.

Fearless prediction: In 5 years, the MCP-esque hegemony of Microsoft will be broken. Microsoft will basically be a company making desktop operating systems for enterprises and will have lost its stranglehold on the consumer market. Apple, by being cautious and consumer-focused with regard to DRM, will be on top. Linux will be in the position Mac OS X is now: a niche player with a significant niche. The niche will be different, of course: you'll see Linux on low-end Chinese and Taiwanese hardware. Think the Fry's Electronics "Great Quality" (heh) 200 buck Chuck computers. Expect Apple to license Mac OS X sparingly to big players like Dell and HP that want to keep in the consumer market, on their high-end stuff. Dell and HP's low-end stuff will be on Linux.

What if Operating Systems were Airlines?
This old standby is here updated for 1999... Air DOS Everybody pushes the airplane until it glides; then they jump on and let the plane coast until it hits the ground again. They then push again, jump on again, and so on...

Mac Airlines
All the stewards, captains, baggage handlers, and ticket agents look and act exactly the same. Every time you ask questions about details, you are gently but firmly told that you don't need to know, don't want to know, and everything will be done for you without your ever having to know, so just shut up.

Windows Air (now Windows XP)
The airport terminal is pretty and colourful, with friendly stewards, easy baggage check and boarding, and a smooth take-off. After about 10 minutes in the air the plane explodes with no warning whatsoever.

Fly NT (now Vista)(pre-release)
The passengers march out onto the runway, say the password in unison, and form the outline of an airplane. Then they all sit down and make a whooshing sound just like they were really flying.

NT Air (now Vista)(post-release)
Just like Windows Air, but costs more, uses much bigger planes, and takes out all the other aircraft within a 40-mile radius when it explodes.

UNIX Airways
Everyone brings one piece of the plane along when they come to the airport. They all go out on the runway and put the plane together piece by piece, arguing non-stop about what kind of plane they are supposed to be building.

Linux Air
Disgruntled employees of all the other OS airlines decide to start their own airline. They build the planes, ticket counters, and pave the runways themselves. They charge a small fee to cover the cost of printing the ticket, but you can also download and print the ticket yourself. When you board the plane, you are given a seat, four bolts, a wrench and a copy of the seat-HOWTO.html. Once settled, the fully adjustable seat is very comfortable, the plan leaves and arrives on time without a single problem, the in-flight meal is wonderful. You try to tell customers of the other airlines about the great trip, but all they can say is, "You had to do what with the seat?"

When you take a photo through a crappy optical system like the human eye (it's a ball of jelly, give it a break!) or the atmosphere, the smallest feature you can pick up is limited. It's explained well here. For ground-based astronomy, it's really important.

I guess you could use the blurry picture and match that, but it'd be more prone to false matches. Put it this way, assume we've a fairly similar skin colour. If you blur your face and mine enough, you couldn't tell us apart. The more similar we look, the less blurring we could allow before a computer couldn't tell us apart.

Adaptive optics coupled with some monster telescopes can give imagery better than Hubble.

But of course saying so won't get anyone some Bush Derangement Syndrome mod points.

To within about one part in 1.E12 the ephemeris second is identical to the SI second defined by the cesium resonance. In 1977 the length of the second of TAI was changed so as to conform better with the preferred definition of the SI second. Before 1977 TAI and UTC ticked faster than they do now. Astronomers did not object to the change in rate of TAI because it was within the uncertainty of the original definition of the ephemeris second.

Can't someone just point a really good telescope up there and get pictures of the stuff left behind?

Unfortunatelly, no, because no such telescope exists. A great explanation of why is at http://www.ucolick.org/~robin/moonhoax.html

Fun facts about civil timekeeping:

- The leap year algorithm can be static because the calendar changes slowly. The corresponding algorithm for time is the 24 hour clock itself, not leap seconds, which are a higher order effect whose equivalent is currently completely ignored (as it should be) for the calendar.

- We don't have leap seconds because the Earth is transferring angular momentum to the lunar orbit. We have leap seconds because the Earth has already slowed down since the 1820 epoch that effectively corresponds to the definition of the SI second.

- We have just passed through a seven year lull in leap seconds. The overall trend is one leap second per 18 months, corresponding to a 2 ms/day mismatch between atomic time and the spinning Earth.

- The length of the mean solar day is growing by about an additional 2 ms per century. As the length of day grows, leap seconds will be required more and more frequently - a quadratic effect. Don't panic, though! The current UTC standard is good for hundreds of years yet.

- The real issue isn't the variability of the Earth's rotation, it is the misidentification of the original definition of the second as 1/86400 of a (varying) mean solar day with the more recent (static) SI unit of time. The original proposal was to call the SI unit an "essen" in honor of a well known (to some) timekeeper.

- When the mean solar day is increased by one full second (hundreds of centuries hence), the moon will have receded by about one mile.

- The day is actually *shorter* now than a hundred years ago, because the long term lunar trend is dwarfed by short term variations that are an order of magnitude larger (see http://www.ucolick.org/~sla/leapsecs/dutc.html).

- Each missed leap second would be equivalent to moving the prime meridian 300 meters at the latitude of Greenwich.

Precise time, and the nature of time, is a subject of particular interest to
the satellite community. A few of you may be aware of a proposal on the
table at the ITU WP-7A to abandon leap seconds. That is, to decouple
what we all think of as "time" from "sundial" time. For thousands of years
solar time has been the basis of civil time with clocks adjusted to make it
so. And for the last 30 years it's been maintained that way by the insertion
of occasional leap seconds into civil time.

The proposal has profound implications, and I cannot possibly do the subject
justice in this forum. You will have to do your own research.

A symposium on the future of UTC was held in May 2003, and is recorded at http://www.ien.it/luc/cesio/itu/ITU.shtml

Much detail can be gleaned from http://www.ucolick.org/~sla/leapsecs/

For a pretty full understanding of what is happening, what has happened, and why, see history of the effort, implications of change, definition of terms

For a pretty full understanding of what is happening, what has happened, and why, see history of the effort, implications of change, definition of terms

For a pretty full understanding of what is happening, what has happened, and why, see history of the effort, implications of change, definition of terms

The name of the telescope is the Thirty Meter Telescope (TMT), as is made clear here on AMEC's page. The main public page for the project is here. In addition to AMEC, the company mentioned in the article, TMT is also a collaboration of the University of California, CalTech, and many others.

First there was the Very Large Telescope.

Then there was the Extremely Large Telescope.

As of a year or so ago, no kidding, they're building the Overwhelmingly Large Telescope (official name).

So what name does this one get?

The Staggeringly Large Telescope? Not as big as "overwhelming". The Astonishingly Large Telescope? Also too small. Ditto for "Frighteningly".

Stupefyingly? Or perhaps the Surpassingly Large Telescope?

The Horrifyingly Large Telescope?

Possibly The Nightmarishly Huge Telescope. Or the Blood-Curdlingly Large Telescope.

The ITU submitted a proposal this year that leap seconds be abandoned.

And if it's tracking UTC, or as the article mentioned, local solar time, then it doesn't have to deal with stupid things like daylight savings time.

"My game is like the pythagorean theorem. No one has an answer."
-Shaquille O'Neal [link

over the past 30 years (coincidentally since the inception of leap seconds) the rotation of the earth's crust has accelerated. This acceleration is apparently due to changes of fluid circulation in the outer core of the earth. Historical investigations of earth rotation indicate that such accelerations are not unprecedented, and it should not be possible for the acceleration to continue for very many more years.

I had the wonderful experience of being an undergraduate in astrophysics at UC Santa Cruz, where a grant in adaptive optics was paving the way for ground-based telescopes. By shining a laser straight where the telescope is pointed, aberrations and distortions from the atmosphere can be measured and exactly countered by the telescope, effectively cancelling atmospheric effects to a remarkable degree. Check out http://cfao.ucolick.org./ The main telescope was outside of San Jose, CA, which might seem a strange location for a telescope due to its proximity to a large city. But since all of the streetlamps in San Jose are sodium (whose spectral properties are well known and simple), those features can be subtracted from any measured spectra and in conjunction with adaptive optics, the telescope outside northern california's largest city produces world-class astronomy. This telescope being built should be pretty neat. I wonder how they will deal with gravitational aberrations. Plus scientists won't ever need to face the threat of government letting their instrument "deorbit" while still producing good data.