Comment by doctoboggan
2 days ago
What causes the unpredictability in this? I would have guessed we have earth's rotation and orbit down to many decimals. Does geological activity, weather, or something else cause rotation speed differences that we just can't predict?
In short, yes, the weather, geology, and signicantly, human movement of water via aquifer draining and dam building, as well as glaicial and ice melts, all contribute to unpredictable changes in the earths rotational period, as well as the axis of rotation. The models for this are IIRC trigonometric polynomials of fairly low order, so even if we could model the unpredictability perfectly, truncation error would limit our ability to distribute the model at super high accuracy. The existing models are built in to, eg, satellites, so you can't just make them arbitrarily complex.
Fun fact: leap seconds will stop being a thing soonish. I think they phase out in 2035, with a delay because Russia needed time to update glonass satellites.
(Note: on mobile, this is from memory, details need checking ;))
2035 is the agreed drop dead date.
Everybody agreed that "Leap seconds" are a sufficiently bad idea that they should be replaced by 2035. Nobody has agreed how to fix it, and "Just turn them off" isn't technically legal. However, "What if there were Leap hours instead?" is technically legal and of course those hours would happen in the very distant future (likely after our civilisation is gone) so it's functionally identical to "Just turn them off" but without legal problems.
Now, I'm English, and England loves this sort of hack. You may have heard that controversial UK politician Nigel Farage "resigned" as a Westminster MP recently and that's not technically true because you can't resign, historically people hated that job and so you can't resign and we never changed that, but what you can do, and everybody does, is get assigned an "Office of profit" in which legally the King is paying you, an MP can't work for the King so you can't be an MP any more. The "Offices of profit" in question aren't real jobs† and don't pay real money, like this "Leap Hour" they'd be a legal fiction. So everybody says you "resigned" but in fact you legally can't do that...
† I mean, historically they were real jobs that made sense which is why the King paid somebody to do them, but England is very, very old so they haven't made sense for centuries and serve only as a legal fiction today.
On the subject of amusing British political legislation, should he defeat Nigel Farage in the resulting by-election Count Binface will not be able to wear his costume in Parliament; not only is business attire required in the House of Commons, it's specifically forbidden to wear a suit of armour there due to a law from the 14th century.
For those unaware, the major parties have declined to participate in the by-election triggered by Farage's resignation seeing the whole thing as a farce. As a result Farage will likely face only Count Binface, a space warrior from Sigma Six. He'd get my vote purely on the basis that he's promised to bring back Ceefax, and build at least one affordable house.
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Leap minutes. You only change your clock when you have accumulated a minute of error. Then you only need to change it once per century
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What does "technically legal" mean here, what authority is that coming from?
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So, it's solving a real problem, why are we dropping it? I mean, why does everybody agree it's a bad solution?
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just move the prime meridian. the one we use for timekeeping doesn't have to aligh with longitude forever.
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> Now, I'm English, and England loves this sort of hack
The 999 year lease to essentially make land practically freehold is one.
https://en.wikipedia.org/wiki/999-year_lease
It's caused significant controversy in my (former colony) country where all other long-term leases are 99 years. The landowners are insisting that their ancestors were cheated and they want their land back.
What a weird tangent
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Everybody agreed that "Leap seconds" are a sufficiently bad idea
No. Not everybody. I prefer accurate time, and all the complaints I've heard hold little water.
My servers need to timesync forwards and back all the time, eg timedrift. They need to jump to new times, or slowly drift, depending.
VMs can be hypervisor starved, or need to move to a new host.
Servers also need to handle missing time. Any daemon or program which cannot handle this is buggy, broken, and needs to deal.
Leap seconds are just part of all of this, and present no new issues compared to normal time change. I question the capabilities of any engineer who singles out time second as difficult to deal with, time is constantly changing on servers. Constantly.
So back to the start, no... everybody doesn't agree. Google isn't "everybody".
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Farage is such an ass, the King should make him feed donkeys or something.
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> as well as the axis of rotation
A frightening fact, the 2011 magnitude 9.0 Tohoku Earthquake shifted the position of the Earth's figure axis about 17 centimeters, making days about 1.8 microseconds shorter.
Phasing out leap seconds is such a crack pot idea. Read the resolution [1]. The conclusion hinges entirely on accepting the immutability of these 2 premises:
I accept all the other premises from the resolution, but then the obvious conclusion should be to just recommend TAI instead of UTC for any application that could be disrupted by leap seconds, instead of butchering UTC and turning it into just a worse version of TAI.
[1]: https://www.bipm.org/en/cgpm-2022/resolution-4
> The models for this are IIRC trigonometric polynomials of fairly low order, so even if we could model the unpredictability perfectly, truncation error would limit our ability to distribute the model at super high accuracy. The existing models are built in to, eg, satellites, so you can't just make them arbitrarily complex.
What are the satellites doing with the models? They're not deciding leap seconds on their own, I hope. So I don't see why the leap second decision would be locked to low accuracy.
Also I would expect doubling the precision to give you a 3-4x slowdown on the math or adding orders to have less effect, and the amount of available computation spent on those models to be like a tenth of a percent at most, so the extra cycles wouldn't be an issue. What am I missing here?
To me it seems like unpredictability is the only real issue.
> because Russia needed time to update glonass satellites.
Why is this? As leap seconds don’t occur on a regular frequency, I assume they are not hardcoded on the software or hardware on board, but the control centre uploads them on the satellites enough in advance once they have been scheduled. So why can’t the control centre just stop sending those updates?
My understanding the problem is that GLONASS is aware of leap seconds at all. It sends messages in UTC, which has this leap second funny business. GPS uses a special "GPS time" (sometimes abbreviated UT) that doesn't have a leap second. For further confusion, the leap second ensures that UTC is never more than 0.9 seconds off of mean solar time, aka UT1.
This type of assumption that was made early in a massive software and hardware project that's now been ossified for ~50 years is going to be hard to change.
> Russia needed time to update glassnoss satellites
GLONASS maybe? or really glasnost era satellites?
Glonass is correct. On mobile, thanks for the correction.
I prefer ephemeris time
A butterfly flaps its wings in Tokyo and we lose a leap second.
Yes, all of those and more. Our measurement precision is much better than the year-to-year first and second derivatives of day length. https://datacenter.iers.org/singlePlot.php?plotname=Bulletin... has the most relevant plot to this; the vertical jumps reflect leap seconds. (IERS has other plots for other dimensions of rotation, but I like this one.)
Very interesting, I wonder what happened in 2020 that causes the rotational speed to start drifting the other way?
Pandemic -> more people working from home -> less people in tall office buildings -> faster rotation (like a skater pulling in their arms).
Probably not remotely true but it would be funny.
Seems like the seasonal change in June-October increased
My best guess would be it's somehow related to water distribution? More water going into the atmosphere? Glaciers growing (unlikely)? Did multiple huge water reservoirs go into service and get filled up over the summer months?
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Since I was checking the Wikipedia article anyway (for when the last leap second was inserted), it also has an answer for this:
"Because the Earth's rotational speed varies in response to climatic and geological events, UTC leap seconds are irregularly spaced and not precisely predictable."
https://en.wikipedia.org/wiki/Leap_second
Quite the opposite. The earth's rotation can vary by quite a few seconds each year. But over hundreds of years, the variations mostly cancel out, which is why I think trying to add or remove leap seconds are a bad idea. The only people who care about such things are space agencies, and they can apply whatever offset they want, it doesn't need to affect everyone else.
Arguably, the only real-world impact this drift has on normal people is GPS, but GPS already transmits an offset from its own clock so that receivers can correct for that. The GPS clock is different both from UTC and TIA.
> the variations mostly cancel out
I don't think we know this do we? we haven't been measuring accurately enough for long enough to be confident that it does in fact cancel out. In fact for the period of time where we've been applying leap seconds they were happening with significant frequency and always in the same direction. It's only been very recently that there's been the realistic suggestion it might drift in the other direction.
If anything people have been suggesting that if we do get rid of leap seconds that we can just wait until the offset is enormous instead (say an hour) because it would take a very long time to happen. But even still, that does actually affect everyday people (because people would surely notice when solar noon is an hour later/earlier). Although pragmatically the obvious solution there is to change timezone instead.
Among other things, turbulent currents of liquid iron in the Earth's core can make the core drift eastward or westward, which causes the crust and mantle to turn slower or faster. Same thing with the strength of the jet stream.
See https://en.wikipedia.org/wiki/Leap_second#:~:text=Other%20co...
Yes. Geological activity, movement in the outer core, atmosphere, oceanic currents, melting ice, earthquakes, to name a few.
Earths rotation has been unusually fast lately. So there is not enough drift to warrant a leap second.
Even the migrations of animals can impact it, although they usually cancel out over the course of a year I think.
I predict there will be a news story or broadcast news pundit who blames this on climate change. bonus points if it winds up on dytime talk shows
Well melting ice certainly go tributes