4 ms·

> The different time definitions exist to support different use cases. UTC isn't flawed, in fact the adjustments that keep it aligned to solar time are very hel

> The different time definitions exist to support different use cases. UTC isn't flawed, in fact the adjustments that keep it aligned to solar time are very helpful for its defined use cases. The user above listed several explicit cases that seem needlessly complicated. Can you give examples where the adjustments to UTC are so helpful for its defined use case? Or elaborate what that case is? I'm not trying to be obstinate - it's just that without examples your response boils down to "No it's not" without further support. I'm open to being convinced...convince me.

jhayward 7y ago
We humans almost always want our concept of "what time is it" to correspond to the relative motion of the sun in the sky. We ask "what time is sunrise?", and "when will the days start getting longer?". We like "noon" to be when the sun is highest in the sky. All those things are what UTC is designed for.
- ergothus 7y ago
  And the leap seconds meaningfully alter that?
  - lutorm 7y ago
    Yes. Leap seconds are there to align UTC (an atomic time) with UT1, which is defined based on mean solar time, ie "the day", since UT1 isn't uniform. Without leap seconds, UTC will slowly drift out of sync with the Earth's rotation.
    - ergothus 7y ago
      That's the point though. The above post said leap seconds cause more harm than good - a correction done once a century would fit well enough within the purpose you've defined here. If UTC is out of sync with the sun by less than a minute, no human will notice, and non-humans don't care about the sun and are happier with fewer disruptions.
- msla 7y ago
  > We ask "what time is sunrise?", and "when will the days start getting longer?". We like "noon" to be when the sun is highest in the sky. All those things are what UTC is designed for. The first thing is for time zones, inclusive of DST/Summer Time/etc. The second thing is for calendrical reform, which we've basically stopped doing now that the Gregorian calendar is as widespread as it's going to be. Leap seconds are for this: https://tycho.usno.navy.mil/leapsec.html https://tycho.usno.navy.mil/leapsec.html > Currently the Earth runs slow at roughly 2 milliseconds per day. After 500 days, the difference between the Earth rotation time and the atomic time would be 1 second. Instead of allowing this to happen, a leap second is inserted to bring the two times closer together. The "error" induced by the Earth slowing amounts to 12 minutes over the course of one thousand years.
- toast0 7y ago
  Solar noon varies from 11:53 in November to 12:23 in February where I live (it keeps closer to the hour during DST [1]); an adjustment of 37 seconds doesn't seem to be very big compared to the 30 minute swing we observe over the year. It seems more reasonable to wait until the gap gets large enough to coordinate an hour jump in clocks with enough advance notice that there's a good chance of having it happen simultaneously. At the rate of leap seconds in the last 60 years, that should be several thousand years away; hopefully none of my software is running then. [1] I'll save the rant on DST.
- twic 7y ago
  We humans, without the use of a clock, do not have the faintest idea when midday or midnight is. We can't judge when the sun is highest in the sky, and we certainly can't judge when it's lowest under our feet. The sun isn't even highest in the sky at noon! Firstly because of timezones (your noon is based on highest-sun in the middle of your timezone, not your current longitude), and secondly because of this whole epicyclic botheration: https://en.wikipedia.org/wiki/Equation_of_time https://en.wikipedia.org/wiki/Equation_of_time
  - InitialLastName 7y ago
    We sure can judge whether it's before or after sunset though.
    - twic 7y ago
      Nope. Is sunset when the lower limb of the sun touches the horizon? When it's halfway? When it disappears completely? And is that the actual horizon where the sun happens to be today? The treeline above it? The tower block in the way? Where sea level would be if there wasn't land there? Or just when it gets dark? But then is that civil twilight? Nautical twilight? Astronomical twilight? When the light from the sun gets dimmer than the light from the streetlights that happen to be in your area?
  - bacon_waffle 7y ago
    I've been surprised at how "in tune" I've become to time, at times, when I've lived outside for substantial periods. Certainly it's not hard to have better than the "faintest idea" when midday or midnight is, if +/- 30 minutes qualifies? Plenty good to decide when to have lunch... In the higher latitudes, it requires even less acclimation once you've got an idea of your orientation, and maybe what the stars look like. To the point that, at the poles, a clear sky is a direct-reading 24-hour clock.
FabHK 7y ago
I think most applications (including computers, except GPS receivers internally) should just switch to UT1. A rotation of the earth takes a day, and a day has 86400 seconds. Done. (Fine, a second is not exactly an SI second, but close enough for most practical purposes, and computers can handle it.)

jhayward 7y ago

We humans almost always want our concept of "what time is it" to correspond to the relative motion of the sun in the sky. We ask "what time is sunrise?", and "when will the days start getting longer?". We like "noon" to be when the sun is highest in the sky. All those things are what UTC is designed for.

ergothus 7y ago
And the leap seconds meaningfully alter that?
- lutorm 7y ago
  Yes. Leap seconds are there to align UTC (an atomic time) with UT1, which is defined based on mean solar time, ie "the day", since UT1 isn't uniform. Without leap seconds, UTC will slowly drift out of sync with the Earth's rotation.
  - ergothus 7y ago
    That's the point though. The above post said leap seconds cause more harm than good - a correction done once a century would fit well enough within the purpose you've defined here. If UTC is out of sync with the sun by less than a minute, no human will notice, and non-humans don't care about the sun and are happier with fewer disruptions.
msla 7y ago
> We ask "what time is sunrise?", and "when will the days start getting longer?". We like "noon" to be when the sun is highest in the sky. All those things are what UTC is designed for. The first thing is for time zones, inclusive of DST/Summer Time/etc. The second thing is for calendrical reform, which we've basically stopped doing now that the Gregorian calendar is as widespread as it's going to be. Leap seconds are for this: https://tycho.usno.navy.mil/leapsec.html https://tycho.usno.navy.mil/leapsec.html > Currently the Earth runs slow at roughly 2 milliseconds per day. After 500 days, the difference between the Earth rotation time and the atomic time would be 1 second. Instead of allowing this to happen, a leap second is inserted to bring the two times closer together. The "error" induced by the Earth slowing amounts to 12 minutes over the course of one thousand years.
toast0 7y ago
Solar noon varies from 11:53 in November to 12:23 in February where I live (it keeps closer to the hour during DST [1]); an adjustment of 37 seconds doesn't seem to be very big compared to the 30 minute swing we observe over the year. It seems more reasonable to wait until the gap gets large enough to coordinate an hour jump in clocks with enough advance notice that there's a good chance of having it happen simultaneously. At the rate of leap seconds in the last 60 years, that should be several thousand years away; hopefully none of my software is running then. [1] I'll save the rant on DST.
twic 7y ago
We humans, without the use of a clock, do not have the faintest idea when midday or midnight is. We can't judge when the sun is highest in the sky, and we certainly can't judge when it's lowest under our feet. The sun isn't even highest in the sky at noon! Firstly because of timezones (your noon is based on highest-sun in the middle of your timezone, not your current longitude), and secondly because of this whole epicyclic botheration: https://en.wikipedia.org/wiki/Equation_of_time https://en.wikipedia.org/wiki/Equation_of_time
- InitialLastName 7y ago
  We sure can judge whether it's before or after sunset though.
  - twic 7y ago
    Nope. Is sunset when the lower limb of the sun touches the horizon? When it's halfway? When it disappears completely? And is that the actual horizon where the sun happens to be today? The treeline above it? The tower block in the way? Where sea level would be if there wasn't land there? Or just when it gets dark? But then is that civil twilight? Nautical twilight? Astronomical twilight? When the light from the sun gets dimmer than the light from the streetlights that happen to be in your area?
- bacon_waffle 7y ago
  I've been surprised at how "in tune" I've become to time, at times, when I've lived outside for substantial periods. Certainly it's not hard to have better than the "faintest idea" when midday or midnight is, if +/- 30 minutes qualifies? Plenty good to decide when to have lunch... In the higher latitudes, it requires even less acclimation once you've got an idea of your orientation, and maybe what the stars look like. To the point that, at the poles, a clear sky is a direct-reading 24-hour clock.

FabHK 7y ago

I think most applications (including computers, except GPS receivers internally) should just switch to UT1. A rotation of the earth takes a day, and a day has 86400 seconds. Done. (Fine, a second is not exactly an SI second, but close enough for most practical purposes, and computers can handle it.)