13 ms·

This periodic adjustment mainly benefits scientists and astronomers as it allows them to observe celestial bodies using UTC for most purposes This is incorrect

This periodic adjustment mainly benefits scientists and astronomers as it allows them to observe celestial bodies using UTC for most purposes This is incorrect, dealing with leap seconds is a major problem in astronomy, requiring a data file or even recompile any time there is a new one announced. Since they are only ever announced 6 months in advance, it creates a lot of logistical problems. Astronomy algorithms usually work in Barycentric Dynamic Time, or Terrestrial Time, or UT1. In reality the whole invention of UTC is so that people don't have to deal with those systems on a daily basis. The process most astronomy programs go through is to get the UTC from the user, convert the Gregorian date to a Julian day number to get rid of the Gregorian Calendar altogether. Then look up the number of leap seconds, add those to the JD to get International Atomic Time, then add 32.184 seconds to get Terrestrial Time. If Barycentric Dynamic Time is needed, you must first compute the velocity of the Earth relative to the solar system barycenter (which itself requires TDB), then compute the relativistic effects of that motion on Terrestrial Time. If you need UT1, these can only be obtained by observation from the International Earth Rotation Service, and required daily updates, and interpolation of values in between observations. So, as you can see, leap seconds do nothing to make an astronomer's life easier. In fact, we jump through a lot of hoops to make the average person's life easier. It sounds like Meta wants to change the definition of time for everyone just to make their programming a little easier. I find the very premise just out right ridiculous. It's true that your average person will not be affected by the Sun setting a few seconds earlier. But eventually it will build up enough error that it eventually has to be addressed, and Meta is just trying to make their problem someone else's problem.

exabrial 4y ago
> Meta is just trying to make their problem someone else's problem. Business as usual
- a9h74j 4y ago
  MAT -- Meta Adjusted Time. AFAIK 'mat' is also a [Sanskrit??] word for truth.
oconnor663 4y ago
The article makes the same point a couple of sentences later: > these days UTC is equally bad for both digital applications and scientists, who often choose TAI or UT1 instead.
- gmiller123456 4y ago
  UTC was never to make astronomy applications easier. The only thing that has changed is that cheap computers make it easier for astronomers to use UTC as a starting point.
  - ncmncm 4y ago
    Then it was for nobody. Astronomers find UTC leap seconds as much a nuisance as everybody else.
willis936 4y ago
It's not just a headsche for Meta's programmers. Anyone involved with bookkeeping and synchronizing has an unnecessary bugbear to deal with. Every six months is simply too often. If it was switched to an adjustment made every 2-10 decades with at least a decade to update the file then the problem would be greatly lessened.
- aeyes 4y ago
  Why is this too often? We already need to update tzdata continuously. The problem is that it is not often enough to force you to have a good process in place.
  - vbezhenar 4y ago
    So another option is to adjust to 1/100 second every few months, so good processes will have to appear, one way or another.
    - nullc 4y ago
      > So another option is to adjust to 1/100 second every few months That's pretty awful. We have a lot of systems now which care about duration. Any scheme that makes a time span unpredictable will cause problems. Doing it more often means more problems. The only improvement is that you hope that the things that care about 1/100th of a second differences are rare enough that disturbing thing many times more often is a good tradeoff. This isn't a good bet especially because at time goes on we build faster and more stable systems that care about tighter and tighter synchronization.
  - willis936 4y ago
    Because tzdata is based off of political boundaries and decisions. If I'm making a dataset that needs continuous timestamps for multiple decades then UTC is effectively off the table because of how under-specified and poorly implemented leap seconds are in various software. So what's left is TAI and GPS, fine enough but now users see the timestamped data as being several seconds off. So we use a translation layer but some HMIs don't allow that so it's best to just not do it at all. This reality is not unique. Thousands of engineers have walked down this path and asked "why?".
jefftk 4y ago
> So, as you can see, leap seconds do nothing to make an astronomer's life easier. In fact, we jump through a lot of hoops to make the average person's life easier. It sounds like Meta wants to change the definition of time for everyone just to make their programming a little easier. I find the very premise just out right ridiculous. Meta (and everyone else behind this proposal) are arguing that leap seconds are more trouble than they're worth. Just as you are in the specific case of astronomy.
- wumpus 4y ago
  Knowing where the Earth is is vitally important for much of astronomy. You can't point at something small in the sky without knowing it. Personally, I think we should return to the Julian calendar. Leap years are too complicated otherwise, not worth the trouble.
- gmiller123456 4y ago
  All I did was make the argument that they didn't make an astronomer's life easier, at no point did I say it was more trouble that it's worth.
  - alecbz 4y ago
    You also said: > It sounds like Meta wants to change the definition of time for everyone just to make their programming a little easier. I find the very premise just out right ridiculous. ... Meta is just trying to make their problem someone else's problem. Meta's argument is: we should get rid of leap seconds because even though they're helpful for astronomers, they're bad for everyone else. Your counterpoint was: Actually leap seconds are _also_ bad for astronomers. Which implies then that Meta is even more right to suggest that we get rid of leap seconds, because it seems like they help nobody.
    - gmiller123456 4y ago
      I can see how you'd read it that way, but my point was that they were not invented for astronomers, with the implication being the author didn't research the topic thoroughly enough to be making recommendations.
lucb1e 4y ago
for anyone else wondering about TDB: > Barycentric Dynamical Time (TDB, from the French Temps Dynamique Barycentrique)
salty_biscuits 4y ago
I always heard that the main reason for the leap second was that the british didn't want the prime meridian moving away from Greenwich (i.e. it is a weird political thing).
- revertmean 4y ago
  The prime meridian has actually shifted hundreds of feet from the original line already. It's not really where they show you at the observatory any more.
- denton-scratch 4y ago
  You heard wrong. And introduction of leap-seconds wouldn't have made a blind bit of difference to the location of the prime meridian.
yunohn 4y ago
Even NIST (1) claims that leap seconds are added to sync UTC with IAT. Your point is that astronomical systems don’t use IAT directly but instead start with UTC and convert across various other systems? Could be, but then the purpose of UTC syncing was lost somewhere. Any idea why? (1) https://www.nist.gov/pml/time-and-frequency-division/leap-seconds-faqs https://www.nist.gov/pml/time-and-frequency-division/leap-se...
- zokier 4y ago
  Navy celestial navigation. Naval almanacs by necessity were based on rotation of earth, so that was the timescale that naval organizations broadcast across the earth to support their ships. Eventually that radio broadcast time morphed into UTC, and then was repurposed as general-purpose civil time.
emmelaich 4y ago
That's in the article! > While the leap second might have been an acceptable solution in 1972, when it made both the scientific community and the telecom industry happy, these days UTC is equally bad for both digital applications and scientists, who often choose TAI or UT1 instead.
- thrown_22 4y ago
  What's not in the article is why TAI is not mandated to be used in facebook it UTC is so difficult for them to get right.
  - IshKebab 4y ago
    Nothing supports TAI.
    - thrown_22 4y ago
      Oh no, imagine having to write software to fix your problems as a software developer.
      - IshKebab 4y ago
        Sure I'll just write and submit patches to every piece of server software used by Facebook. Very practical.
brandmeyer 4y ago
> If you need UT1, these can only be obtained by observation from the International Earth Rotation Service, and required daily updates, and interpolation of values in between observations. The GPS CNAV messages (on L2C and L5) have support for the Earth orientation parameters, but GPS isn't broadcast those messages yet. Maybe we'll get them with the OCX deployment. BeiDou 3 is transmitting the Earth orientation parameters now. So this one tiny bit of your headache will get easier in the near future as receivers start to forward these data along.
tablespoon 4y ago
> It sounds like Meta wants to change the definition of time for everyone just to make their programming a little easier. I find the very premise just out right ridiculous. It's also incredibly common attitude amongst software engineers and software engineering organizations. "Simplify" often means push complexity off of us and onto others. > ...Meta is just trying to make their problem someone else's problem. Exactly right.
ssivark 4y ago
Further, if someone thinks it’s already a pain to adapt systems for leap seconds, imagine the pain of ignoring this for decades/centuries and then having to deal with a massive headache on the scale of the feared Y2K problem. In the spirit of continuous integration and “releasing often” and “let it crash” on smaller scales, leap seconds seem like a pretty good solution for robustness at the global systemic level.
nl 4y ago
Actually one of the few objections to dropping the leap second at the previous review in 2015 did come from the International Astronomical Union (IAU). Their report says: Some members of the astronomical community have expressed great concern over any change to the current system. These concerns are based on the use of existing software that takes advantage of the current definition and uses UTC as a substitute for UT1. Their requirements for precision are such that the current 0.9-second tolerance is adequate, and their software has been designed accordingly. Should the definition of UTC be modified in any way that would permit this tolerance to be exceeded, they anticipate it would create a substantial cost to make non-trivial changes in existing software. Some members of the astrodynamic community have voiced similar concerns regarding legacy software used in the determination of orbital parameters of artificial satellites that again utilizes UTC as a substitute for UT1.[1] So I'd suggest the FB summary of their objections is pretty much correct. Reading the report completely, it seems the IAU wants to create a new time standard (not UTC) that drops the leap second and keep UTC as it is: It was suggested that a means of transitioning to a uniform time scale could be accomplished by the creation of another time scale that might be called Temps International (TI) to clearly distinguish it from Universal Time. [1] https://www.atnf.csiro.au/iau-comm31/pdf/ContDoc-010_IAU_060710.pdf https://www.atnf.csiro.au/iau-comm31/pdf/ContDoc-010_IAU_060...
skwheel 4y ago
Yes, I fully support this position by Meta but their reasoning is not quite right when it comes to astronomers and scientists. Passing around a leap second kernel is a major pain for everyone dealing with GPS, satellite ephemerides, celestial bodies, etc. Leap seconds transform a problem which is entirely deterministic, and make it dependent on a policy decided by a committee, like timezones.
mycall 4y ago
I thought "quantum hard drives" and Quantum Astronomy will replace the need for UTC/leap seconds soon.
nullc 4y ago
I made a post about the potential of a negative leapsecond a week ago -- https://news.ycombinator.com/item?id=32125171 https://news.ycombinator.com/item?id=32125171 I was partially motivated to write about leapseconds because I'd spent much of the day trying to construct leapsecond tests for my telescope pointing code. You're absolutely right, leapseconds don't help astronomers. Casual astronomy will do a one star alignment, so in effect they'll point at a star find out where it is and from it effectively compute the UT1 UTC offset (along with correcting other sources of pointing error). This applies no equally for electronic or manual pointing. More serious astronomy with use the IERS Bulletin A data. https://datacenter.iers.org/productMetadata.php?id=6 https://datacenter.iers.org/productMetadata.php?id=6 Without it you UTC would only get you within 0.9 seconds (and you won't know the other polar motion terms), so you might as well just platesolve. If you do have the IERS data you have to then back out leap seconds. You note you need constantly updated tables to do that, but it's worse than that: All over the place systems are getting their UTC replaced with leap-smeared UTC without the operators knowledge. You can't just back out leapsmear especially if you don't know you have it. I'm sure leapseconds sounded like a good idea on paper and when only a small number of especially exotic systems needed to deal with them. But the pervasive computerization since the 1960s has increased the cost of leapseconds by many orders of magnitude. > But eventually it will build up enough error that it eventually has to be addressed Yes, in 4000 years or so people can adopt new timezones that are shifted over by an hour. We already have comprehensive support for timezones, and support for them changing (as they're fairly vulnerable to political whim), computers handle them reasonable well-- and importantly they're primarily a presentation element so they don't mess up precise timekeeping. Maybe in 4000 years no one will even care-- perhaps everyone will have finally switched to SWATCH INTERNET TIME. But regardless, a timezone addition/change every few thousand years is a much better situation than we have with leapseconds.
vorticalbox 4y ago
> Barycentric Dynamic Time This named after bary Centre? https://en.m.wikipedia.org/wiki/Barycenter https://en.m.wikipedia.org/wiki/Barycenter
notorandit 4y ago
Correct time keeping is important whenever you have time-base events. Especially the billing ones. Looong ago, while working on a mobile telphony billing system, we found out that a telephony system by Siemens (Germany, Europe) was creating billing events off by one our when processed by a system by Digital (USA, America) because of different DST switch date.

exabrial 4y ago

> Meta is just trying to make their problem someone else's problem. Business as usual

a9h74j 4y ago
MAT -- Meta Adjusted Time. AFAIK 'mat' is also a [Sanskrit??] word for truth.

oconnor663 4y ago

The article makes the same point a couple of sentences later: > these days UTC is equally bad for both digital applications and scientists, who often choose TAI or UT1 instead.

gmiller123456 4y ago
UTC was never to make astronomy applications easier. The only thing that has changed is that cheap computers make it easier for astronomers to use UTC as a starting point.
- ncmncm 4y ago
  Then it was for nobody. Astronomers find UTC leap seconds as much a nuisance as everybody else.

willis936 4y ago

It's not just a headsche for Meta's programmers. Anyone involved with bookkeeping and synchronizing has an unnecessary bugbear to deal with. Every six months is simply too often. If it was switched to an adjustment made every 2-10 decades with at least a decade to update the file then the problem would be greatly lessened.

aeyes 4y ago
Why is this too often? We already need to update tzdata continuously. The problem is that it is not often enough to force you to have a good process in place.
- vbezhenar 4y ago
  So another option is to adjust to 1/100 second every few months, so good processes will have to appear, one way or another.
  - nullc 4y ago
    > So another option is to adjust to 1/100 second every few months That's pretty awful. We have a lot of systems now which care about duration. Any scheme that makes a time span unpredictable will cause problems. Doing it more often means more problems. The only improvement is that you hope that the things that care about 1/100th of a second differences are rare enough that disturbing thing many times more often is a good tradeoff. This isn't a good bet especially because at time goes on we build faster and more stable systems that care about tighter and tighter synchronization.
- willis936 4y ago
  Because tzdata is based off of political boundaries and decisions. If I'm making a dataset that needs continuous timestamps for multiple decades then UTC is effectively off the table because of how under-specified and poorly implemented leap seconds are in various software. So what's left is TAI and GPS, fine enough but now users see the timestamped data as being several seconds off. So we use a translation layer but some HMIs don't allow that so it's best to just not do it at all. This reality is not unique. Thousands of engineers have walked down this path and asked "why?".

jefftk 4y ago

> So, as you can see, leap seconds do nothing to make an astronomer's life easier. In fact, we jump through a lot of hoops to make the average person's life easier. It sounds like Meta wants to change the definition of time for everyone just to make their programming a little easier. I find the very premise just out right ridiculous. Meta (and everyone else behind this proposal) are arguing that leap seconds are more trouble than they're worth. Just as you are in the specific case of astronomy.

wumpus 4y ago
Knowing where the Earth is is vitally important for much of astronomy. You can't point at something small in the sky without knowing it. Personally, I think we should return to the Julian calendar. Leap years are too complicated otherwise, not worth the trouble.
gmiller123456 4y ago
All I did was make the argument that they didn't make an astronomer's life easier, at no point did I say it was more trouble that it's worth.
- alecbz 4y ago
  You also said: > It sounds like Meta wants to change the definition of time for everyone just to make their programming a little easier. I find the very premise just out right ridiculous. ... Meta is just trying to make their problem someone else's problem. Meta's argument is: we should get rid of leap seconds because even though they're helpful for astronomers, they're bad for everyone else. Your counterpoint was: Actually leap seconds are _also_ bad for astronomers. Which implies then that Meta is even more right to suggest that we get rid of leap seconds, because it seems like they help nobody.
  - gmiller123456 4y ago
    I can see how you'd read it that way, but my point was that they were not invented for astronomers, with the implication being the author didn't research the topic thoroughly enough to be making recommendations.

lucb1e 4y ago

for anyone else wondering about TDB: > Barycentric Dynamical Time (TDB, from the French Temps Dynamique Barycentrique)

salty_biscuits 4y ago

I always heard that the main reason for the leap second was that the british didn't want the prime meridian moving away from Greenwich (i.e. it is a weird political thing).

revertmean 4y ago
The prime meridian has actually shifted hundreds of feet from the original line already. It's not really where they show you at the observatory any more.
denton-scratch 4y ago
You heard wrong. And introduction of leap-seconds wouldn't have made a blind bit of difference to the location of the prime meridian.

yunohn 4y ago

Even NIST (1) claims that leap seconds are added to sync UTC with IAT. Your point is that astronomical systems don’t use IAT directly but instead start with UTC and convert across various other systems? Could be, but then the purpose of UTC syncing was lost somewhere. Any idea why? (1) https://www.nist.gov/pml/time-and-frequency-division/leap-seconds-faqs https://www.nist.gov/pml/time-and-frequency-division/leap-se...

zokier 4y ago
Navy celestial navigation. Naval almanacs by necessity were based on rotation of earth, so that was the timescale that naval organizations broadcast across the earth to support their ships. Eventually that radio broadcast time morphed into UTC, and then was repurposed as general-purpose civil time.

emmelaich 4y ago

That's in the article! > While the leap second might have been an acceptable solution in 1972, when it made both the scientific community and the telecom industry happy, these days UTC is equally bad for both digital applications and scientists, who often choose TAI or UT1 instead.

thrown_22 4y ago
What's not in the article is why TAI is not mandated to be used in facebook it UTC is so difficult for them to get right.
- IshKebab 4y ago
  Nothing supports TAI.
  - thrown_22 4y ago
    Oh no, imagine having to write software to fix your problems as a software developer.
    - IshKebab 4y ago
      Sure I'll just write and submit patches to every piece of server software used by Facebook. Very practical.

brandmeyer 4y ago

> If you need UT1, these can only be obtained by observation from the International Earth Rotation Service, and required daily updates, and interpolation of values in between observations. The GPS CNAV messages (on L2C and L5) have support for the Earth orientation parameters, but GPS isn't broadcast those messages yet. Maybe we'll get them with the OCX deployment. BeiDou 3 is transmitting the Earth orientation parameters now. So this one tiny bit of your headache will get easier in the near future as receivers start to forward these data along.

tablespoon 4y ago

> It sounds like Meta wants to change the definition of time for everyone just to make their programming a little easier. I find the very premise just out right ridiculous. It's also incredibly common attitude amongst software engineers and software engineering organizations. "Simplify" often means push complexity off of us and onto others. > ...Meta is just trying to make their problem someone else's problem. Exactly right.

ssivark 4y ago

Further, if someone thinks it’s already a pain to adapt systems for leap seconds, imagine the pain of ignoring this for decades/centuries and then having to deal with a massive headache on the scale of the feared Y2K problem. In the spirit of continuous integration and “releasing often” and “let it crash” on smaller scales, leap seconds seem like a pretty good solution for robustness at the global systemic level.

nl 4y ago

Actually one of the few objections to dropping the leap second at the previous review in 2015 did come from the International Astronomical Union (IAU). Their report says: Some members of the astronomical community have expressed great concern over any change to the current system. These concerns are based on the use of existing software that takes advantage of the current definition and uses UTC as a substitute for UT1. Their requirements for precision are such that the current 0.9-second tolerance is adequate, and their software has been designed accordingly. Should the definition of UTC be modified in any way that would permit this tolerance to be exceeded, they anticipate it would create a substantial cost to make non-trivial changes in existing software. Some members of the astrodynamic community have voiced similar concerns regarding legacy software used in the determination of orbital parameters of artificial satellites that again utilizes UTC as a substitute for UT1.[1] So I'd suggest the FB summary of their objections is pretty much correct. Reading the report completely, it seems the IAU wants to create a new time standard (not UTC) that drops the leap second and keep UTC as it is: It was suggested that a means of transitioning to a uniform time scale could be accomplished by the creation of another time scale that might be called Temps International (TI) to clearly distinguish it from Universal Time. [1] https://www.atnf.csiro.au/iau-comm31/pdf/ContDoc-010_IAU_060710.pdf https://www.atnf.csiro.au/iau-comm31/pdf/ContDoc-010_IAU_060...

skwheel 4y ago

Yes, I fully support this position by Meta but their reasoning is not quite right when it comes to astronomers and scientists. Passing around a leap second kernel is a major pain for everyone dealing with GPS, satellite ephemerides, celestial bodies, etc. Leap seconds transform a problem which is entirely deterministic, and make it dependent on a policy decided by a committee, like timezones.

mycall 4y ago

I thought "quantum hard drives" and Quantum Astronomy will replace the need for UTC/leap seconds soon.

nullc 4y ago

I made a post about the potential of a negative leapsecond a week ago -- https://news.ycombinator.com/item?id=32125171 https://news.ycombinator.com/item?id=32125171 I was partially motivated to write about leapseconds because I'd spent much of the day trying to construct leapsecond tests for my telescope pointing code. You're absolutely right, leapseconds don't help astronomers. Casual astronomy will do a one star alignment, so in effect they'll point at a star find out where it is and from it effectively compute the UT1 UTC offset (along with correcting other sources of pointing error). This applies no equally for electronic or manual pointing. More serious astronomy with use the IERS Bulletin A data. https://datacenter.iers.org/productMetadata.php?id=6 https://datacenter.iers.org/productMetadata.php?id=6 Without it you UTC would only get you within 0.9 seconds (and you won't know the other polar motion terms), so you might as well just platesolve. If you do have the IERS data you have to then back out leap seconds. You note you need constantly updated tables to do that, but it's worse than that: All over the place systems are getting their UTC replaced with leap-smeared UTC without the operators knowledge. You can't just back out leapsmear especially if you don't know you have it. I'm sure leapseconds sounded like a good idea on paper and when only a small number of especially exotic systems needed to deal with them. But the pervasive computerization since the 1960s has increased the cost of leapseconds by many orders of magnitude. > But eventually it will build up enough error that it eventually has to be addressed Yes, in 4000 years or so people can adopt new timezones that are shifted over by an hour. We already have comprehensive support for timezones, and support for them changing (as they're fairly vulnerable to political whim), computers handle them reasonable well-- and importantly they're primarily a presentation element so they don't mess up precise timekeeping. Maybe in 4000 years no one will even care-- perhaps everyone will have finally switched to SWATCH INTERNET TIME. But regardless, a timezone addition/change every few thousand years is a much better situation than we have with leapseconds.

vorticalbox 4y ago

> Barycentric Dynamic Time This named after bary Centre? https://en.m.wikipedia.org/wiki/Barycenter https://en.m.wikipedia.org/wiki/Barycenter

notorandit 4y ago

Correct time keeping is important whenever you have time-base events. Especially the billing ones. Looong ago, while working on a mobile telphony billing system, we found out that a telephony system by Siemens (Germany, Europe) was creating billing events off by one our when processed by a system by Digital (USA, America) because of different DST switch date.