4 ms·

> Obviously having 3:30 pm suddenly become the middle of the night would be bad, but we're talking a delta of 18 seconds spread over almost 50 years... hardly b

> Obviously having 3:30 pm suddenly become the middle of the night would be bad, but we're talking a delta of 18 seconds spread over almost 50 years... hardly big enough to be called "out of sync" in any noticeable sense. And the Julian calendar was 'good enough' for a long time… until it wasn't and Pope Gregory XIII had to announce the skipping over of 10 days so that (e.g.) the Spring Equinox actually lined up with the season of spring more accurately. I understand the sentiment of wanting to simplify things, but kicking the can down the road so it's someone else's problem is wrong in my eyes.

iso1631 5y ago
Large parts of the world shift civil time by an hour twice a year. Drifting 1 day every 200,000 years doesn't sound like kicking the can down the road. If human civilisation still exists by the time we've reached just 1 hour of difference we'll be occupying multiple bodies throughout the solar system, if not further afield, and have to have come up with a new time system anyway. Even the length of a second varies because of relativity.
- kijin 5y ago
  Yeah, we already do the Feb 29 thing every 4 years. We make exceptions to that rule every 100 years, and an exception to the exception every 400 years. Those leap years make larger oscillations than any leap second ever tries to correct for, and we're totally fine with that. Adding another exception every 200,000 years doesn't sound unexpected at all.
  - deleted 5y ago
    [deleted]
  - user-the-name 5y ago
    They do not. Those adjust the calendar, not the clock.
    - kijin 5y ago
      A calendar is just a clock that measures longer durations of time.
      - user-the-name 5y ago
        Irrelevant in this context.
      - FabHK 5y ago
        But one of these adjustments aims to keep mid day at noon, while the other aims to keep solstice around 21 Dec. You could skip leap years and still have the sun up at noon, while your solstice date drifts away. Or, you could skip leak seconds and still have the solstice on 21 Dec, but have your noon drift away from mid day.
        iso1631 5y ago
        very few locations have the sun directly above at 12 (based on a timezone offset from UTC), and just as many places have it directly above at 12 based on an offset from TAI The sun is overhead from Greenwich at 12:06 GMT today, it varies by about half an hour from 1143 to 1214 through the year (ignoring daylight saving) I'm not sure if varying from 1150 to 1221 would be any better. Even after a minute of leap seconds (say 100 years) the point where the "sun is overhead at 12:00:00" point for points at UK/Ireland latitude would have moved about 10 miles from its current position. in a few millenia the timezone would be wrong, but easilly corrected by either skipping a "spring forward" or "fall back" time.
  - throw0101a 5y ago
    > Yeah, we already do the Feb 29 thing every 4 years. Except it's not every four years. It's every four years, but it is skipped if the year is divisible by 100… but not skipped if it is also divisible by 400—which ended up biting people in 2000 which was a leap year: * https://slate.com/technology/2016/02/the-math-behind-leap-years.html https://slate.com/technology/2016/02/the-math-behind-leap-ye...
    - JadeNB 5y ago
      > > Yeah, we already do the Feb 29 thing every 4 years. > Except it's not every four years. > It's every four years, but it is skipped if the year is divisible by 100… but not skipped if it is also divisible by 400—which ended up biting people in 2000 which was a leap year …. Unless they edited, that's exactly what your parent said, after you cut off the quote: > Yeah, we already do the Feb 29 thing every 4 years. We make exceptions to that rule every 100 years, and an exception to the exception every 400 years.
- throw0101a 5y ago
  > Large parts of the world shift civil time by an hour twice a year. Yes, and how many things break every time this common thing occurs? Or every four years when February 29 rears its ugly head. And these are code paths that should be well tested because of their frequency.
  - iso1631 5y ago
    POint is we can cope with the sun directly overhead at 14:20 (as it is today in Madrid), or at 11:20 (as it is in Warsaw in November) A drift of a minute over a lifetime makes no difference. We should just use TAI (with timezone offsets) for general time and be done with it. Even today UT1 is widely different to UTC (183ms), so it's not like using UTC is accurate. Why is 183ms an acceptable difference (no leap milliseconds), a couple of hours (timezone sizes), one hour (DST), but we have to correct for 40 seconds each century?
learc83 5y ago
In 100,000 years when 12pm is in the middle of the night, no one is going to care. It will have been that way for all of living memory, and the fact that noon used to be midday will be nothing more than a historical curiosity. The drift is far too slow for anyone to notice.
- icedchai 5y ago
  I've met grown adults that think 12 PM is the middle of the night already. (They don't understand PM vs AM.)
  - JadeNB 5y ago
    > I've met grown adults that think 12 PM is the middle of the night already. (They don't understand PM vs AM.) That's because it doesn't make any sense to describe the middle of the day by '12 PM', since 'PM' should mean "after midday". To be sure we have conventions about this, but not knowing those arbitrary conventions is no reason to think that people don't understand the concept. I think better usage is 12 noon and 12 midnight (https://en.wikipedia.org/wiki/12-hour_clock#Confusion_at_noon_and_midnight https://en.wikipedia.org/wiki/12-hour_clock#Confusion_at_noo... )—though that still requires further disambiguation at midnight (is "midnight on August 3" between August 2 and 3, or between August 3 and 4? I don't know whether there's a common disambiguation here, as with 12 n versus 12 m).
    - nybble41 5y ago
      The inconsistency is in using 12 instead of zero, which results in four discontinuities per day (12:59 AM → 1:00 AM, 11:59 AM → 12:00 PM, 12:59 PM → 1:00 PM, 11:59 PM → 12:00 AM). The times should be divided into 0:00 AM through 11:59 AM and 0:00 PM through 11:59 PM so that the hours wrap around at the AM/PM boundary, not one hour later.
      - JadeNB 5y ago
        > The times should be divided into 0:00 AM through 11:59 AM and 0:00 PM through 11:59 PM so that the hours wrap around at the AM/PM boundary, not one hour later. Sure, although, if we're re-defining how people tell time anyway, we might as well use a 24-hour clock and so avoid the need for AM/PM at all; and, even if we do that, there is still, inevitably, the confusion about on what day 00:00 AM falls. My point was just that not knowing that "12 PM" means noon is a matter of not being aware of an arbitrary convention, rather than of not understanding the concept of AM vs. PM. (Indeed, arguably it is a matter of understanding their meaning all too well!)
Vvector 5y ago
What about leap milliseconds? There are plenty of applications that need millisecond accuracy.
- tialaramex 5y ago
  If you need millisecond accuracy then you definitely don't want UT and so you'd want to avoid leapseconds, not add "leap milliseconds". TAI is very smooth. TAI gives the sort of predictable monotonic clock you might appreciate if you care about milliseconds. One second after another, with a perfect 1000 milliseconds between them, forever. UT is based on a large rock (the planet Earth) spinning. It varies a bunch 'cos the rock is a weird shape and is seismically active so it spins differently over time. If you care about "millisecond accuracy" then you do not want to base that on the spinning of a big rock when you can get a perfectly nice atomic clock and use TAI. If your thought is "But I need millisecond accuracy for my astronomical observations" what you've got there is a big misunderstanding of your context. While UT might seem convenient for figuring out where and when to point telescopes at thing, it's useless for actual time. You need TAI.

iso1631 5y ago

Large parts of the world shift civil time by an hour twice a year. Drifting 1 day every 200,000 years doesn't sound like kicking the can down the road. If human civilisation still exists by the time we've reached just 1 hour of difference we'll be occupying multiple bodies throughout the solar system, if not further afield, and have to have come up with a new time system anyway. Even the length of a second varies because of relativity.

kijin 5y ago
Yeah, we already do the Feb 29 thing every 4 years. We make exceptions to that rule every 100 years, and an exception to the exception every 400 years. Those leap years make larger oscillations than any leap second ever tries to correct for, and we're totally fine with that. Adding another exception every 200,000 years doesn't sound unexpected at all.
- deleted 5y ago
  [deleted]
- user-the-name 5y ago
  They do not. Those adjust the calendar, not the clock.
  - kijin 5y ago
    A calendar is just a clock that measures longer durations of time.
    - user-the-name 5y ago
      Irrelevant in this context.
    - FabHK 5y ago
      But one of these adjustments aims to keep mid day at noon, while the other aims to keep solstice around 21 Dec. You could skip leap years and still have the sun up at noon, while your solstice date drifts away. Or, you could skip leak seconds and still have the solstice on 21 Dec, but have your noon drift away from mid day.
      - iso1631 5y ago
        very few locations have the sun directly above at 12 (based on a timezone offset from UTC), and just as many places have it directly above at 12 based on an offset from TAI The sun is overhead from Greenwich at 12:06 GMT today, it varies by about half an hour from 1143 to 1214 through the year (ignoring daylight saving) I'm not sure if varying from 1150 to 1221 would be any better. Even after a minute of leap seconds (say 100 years) the point where the "sun is overhead at 12:00:00" point for points at UK/Ireland latitude would have moved about 10 miles from its current position. in a few millenia the timezone would be wrong, but easilly corrected by either skipping a "spring forward" or "fall back" time.
- throw0101a 5y ago
  > Yeah, we already do the Feb 29 thing every 4 years. Except it's not every four years. It's every four years, but it is skipped if the year is divisible by 100… but not skipped if it is also divisible by 400—which ended up biting people in 2000 which was a leap year: * https://slate.com/technology/2016/02/the-math-behind-leap-years.html https://slate.com/technology/2016/02/the-math-behind-leap-ye...
  - JadeNB 5y ago
    > > Yeah, we already do the Feb 29 thing every 4 years. > Except it's not every four years. > It's every four years, but it is skipped if the year is divisible by 100… but not skipped if it is also divisible by 400—which ended up biting people in 2000 which was a leap year …. Unless they edited, that's exactly what your parent said, after you cut off the quote: > Yeah, we already do the Feb 29 thing every 4 years. We make exceptions to that rule every 100 years, and an exception to the exception every 400 years.
throw0101a 5y ago
> Large parts of the world shift civil time by an hour twice a year. Yes, and how many things break every time this common thing occurs? Or every four years when February 29 rears its ugly head. And these are code paths that should be well tested because of their frequency.
- iso1631 5y ago
  POint is we can cope with the sun directly overhead at 14:20 (as it is today in Madrid), or at 11:20 (as it is in Warsaw in November) A drift of a minute over a lifetime makes no difference. We should just use TAI (with timezone offsets) for general time and be done with it. Even today UT1 is widely different to UTC (183ms), so it's not like using UTC is accurate. Why is 183ms an acceptable difference (no leap milliseconds), a couple of hours (timezone sizes), one hour (DST), but we have to correct for 40 seconds each century?

learc83 5y ago

In 100,000 years when 12pm is in the middle of the night, no one is going to care. It will have been that way for all of living memory, and the fact that noon used to be midday will be nothing more than a historical curiosity. The drift is far too slow for anyone to notice.

icedchai 5y ago
I've met grown adults that think 12 PM is the middle of the night already. (They don't understand PM vs AM.)
- JadeNB 5y ago
  > I've met grown adults that think 12 PM is the middle of the night already. (They don't understand PM vs AM.) That's because it doesn't make any sense to describe the middle of the day by '12 PM', since 'PM' should mean "after midday". To be sure we have conventions about this, but not knowing those arbitrary conventions is no reason to think that people don't understand the concept. I think better usage is 12 noon and 12 midnight (https://en.wikipedia.org/wiki/12-hour_clock#Confusion_at_noon_and_midnight https://en.wikipedia.org/wiki/12-hour_clock#Confusion_at_noo... )—though that still requires further disambiguation at midnight (is "midnight on August 3" between August 2 and 3, or between August 3 and 4? I don't know whether there's a common disambiguation here, as with 12 n versus 12 m).
  - nybble41 5y ago
    The inconsistency is in using 12 instead of zero, which results in four discontinuities per day (12:59 AM → 1:00 AM, 11:59 AM → 12:00 PM, 12:59 PM → 1:00 PM, 11:59 PM → 12:00 AM). The times should be divided into 0:00 AM through 11:59 AM and 0:00 PM through 11:59 PM so that the hours wrap around at the AM/PM boundary, not one hour later.
    - JadeNB 5y ago
      > The times should be divided into 0:00 AM through 11:59 AM and 0:00 PM through 11:59 PM so that the hours wrap around at the AM/PM boundary, not one hour later. Sure, although, if we're re-defining how people tell time anyway, we might as well use a 24-hour clock and so avoid the need for AM/PM at all; and, even if we do that, there is still, inevitably, the confusion about on what day 00:00 AM falls. My point was just that not knowing that "12 PM" means noon is a matter of not being aware of an arbitrary convention, rather than of not understanding the concept of AM vs. PM. (Indeed, arguably it is a matter of understanding their meaning all too well!)

Vvector 5y ago

What about leap milliseconds? There are plenty of applications that need millisecond accuracy.

tialaramex 5y ago
If you need millisecond accuracy then you definitely don't want UT and so you'd want to avoid leapseconds, not add "leap milliseconds". TAI is very smooth. TAI gives the sort of predictable monotonic clock you might appreciate if you care about milliseconds. One second after another, with a perfect 1000 milliseconds between them, forever. UT is based on a large rock (the planet Earth) spinning. It varies a bunch 'cos the rock is a weird shape and is seismically active so it spins differently over time. If you care about "millisecond accuracy" then you do not want to base that on the spinning of a big rock when you can get a perfectly nice atomic clock and use TAI. If your thought is "But I need millisecond accuracy for my astronomical observations" what you've got there is a big misunderstanding of your context. While UT might seem convenient for figuring out where and when to point telescopes at thing, it's useless for actual time. You need TAI.