4 ms·

Sundials are already ‘wrong’ according to solar time by 30 minutes or more, as an artifact of dividing the world into hour-wide time zones. Astronomy already i

by lesam 4y ago

Sundials are already ‘wrong’ according to solar time by 30 minutes or more, as an artifact of dividing the world into hour-wide time zones. Astronomy already ignores leap seconds in the same way that modern finance ignores half-crowns and shillings.

welterde 4y ago
Astronomy very much relies on the leap seconds. If they ever get abolished it will create lots of headache for all observatories (and hobby astronomers as well), since the telescopes will point more and more incorrectly as UTC drifts away from UT1 (the leap seconds ensure UTC is always within 0.9s of UT1). To explain a bit further: UT1 tracks the Earth's rotation relative to distant quasars and is thus directly the correct clock/reference to use for pointing telescopes. However it doesn't advance at a nice and stable constant frequency, but something that slowly changes over time (and can shift by strong earthquakes) and thus we approximate it with UTC, which runs at a nice constant frequency, but needs occasional correction to match up with Earth's rotation.
- philwelch 4y ago
  I think we can allow astronomers to keep their leap seconds without requiring them to be imposed on the entirety of civil society.
  - welterde 4y ago
    Why should all purpose be removed from UTC if the alternative without leapseconds (TAI) already exists? Just use that if you don't want leap seconds.
    - lovecg 4y ago
      Well, having worked on legacy systems it’s much easier to keep the existing protocol mostly unchanged than migrate the world to a different protocol. Even if the change is as “simple” as subtracting a constant integer everywhere. Just thinking about all the stored timestamps in all databases gives me a headache…
    - ncmncm 4y ago
      Because UTC already has no other purpose than to be what everybody is already using. The leap seconds in UTC benefit literally nobody. But being a standard is a purpose. Changing to TAI means you are different from everybody else, and still have to fool with leap seconds to know what everybody else is using. Worst of all worlds. (Except Google smearing, which is even worse than that.)
      - welterde 4y ago
        That's literally not true, since we astronomers do use UTC as it is intended (since within 0.9s of the correct time is good enough, but being many seconds off isn't anymore for many applications). The argument that the legacy systems should maybe be updated is already being discussed elsewhere, so no need to rehash that.
        ncmncm 4y ago
        If you are doing astronomy with UTC, you are Doing Astronomy Wrong. Have a chat with a colleague. They will set you straight.
        welterde 4y ago
        Hardly. For actually observing with a telescope UT1 is the correct time scale to start the calculation from, since it's directly linked with Earth's rotation - with some complications that you have to calculate local sidereal time and so forth, but this only involves fixed constants; All TAI derived fixed-offset time scales are not linked with Earth's rotation and thus require constantly updated offsets. For most telescopes approximating it with UTC gives good enough results (pointing accuracy wise), so that's what many observatories do. And many smaller and older observatories operate quite a lot of legacy hardware and software that would need to be updated if the current UTC definition were to be changed.
    - zajio1am 4y ago
      Because societal official/legal time is based on UTC and not on TAI. So the point is to change societal official/legal time, not just to use different time standard.

by lesam 4y ago

welterde 4y ago

Astronomy very much relies on the leap seconds. If they ever get abolished it will create lots of headache for all observatories (and hobby astronomers as well), since the telescopes will point more and more incorrectly as UTC drifts away from UT1 (the leap seconds ensure UTC is always within 0.9s of UT1). To explain a bit further: UT1 tracks the Earth's rotation relative to distant quasars and is thus directly the correct clock/reference to use for pointing telescopes. However it doesn't advance at a nice and stable constant frequency, but something that slowly changes over time (and can shift by strong earthquakes) and thus we approximate it with UTC, which runs at a nice constant frequency, but needs occasional correction to match up with Earth's rotation.

philwelch 4y ago
I think we can allow astronomers to keep their leap seconds without requiring them to be imposed on the entirety of civil society.
- welterde 4y ago
  Why should all purpose be removed from UTC if the alternative without leapseconds (TAI) already exists? Just use that if you don't want leap seconds.
  - lovecg 4y ago
    Well, having worked on legacy systems it’s much easier to keep the existing protocol mostly unchanged than migrate the world to a different protocol. Even if the change is as “simple” as subtracting a constant integer everywhere. Just thinking about all the stored timestamps in all databases gives me a headache…
  - ncmncm 4y ago
    Because UTC already has no other purpose than to be what everybody is already using. The leap seconds in UTC benefit literally nobody. But being a standard is a purpose. Changing to TAI means you are different from everybody else, and still have to fool with leap seconds to know what everybody else is using. Worst of all worlds. (Except Google smearing, which is even worse than that.)
    - welterde 4y ago
      That's literally not true, since we astronomers do use UTC as it is intended (since within 0.9s of the correct time is good enough, but being many seconds off isn't anymore for many applications). The argument that the legacy systems should maybe be updated is already being discussed elsewhere, so no need to rehash that.
      - ncmncm 4y ago
        If you are doing astronomy with UTC, you are Doing Astronomy Wrong. Have a chat with a colleague. They will set you straight.
        welterde 4y ago
        Hardly. For actually observing with a telescope UT1 is the correct time scale to start the calculation from, since it's directly linked with Earth's rotation - with some complications that you have to calculate local sidereal time and so forth, but this only involves fixed constants; All TAI derived fixed-offset time scales are not linked with Earth's rotation and thus require constantly updated offsets. For most telescopes approximating it with UTC gives good enough results (pointing accuracy wise), so that's what many observatories do. And many smaller and older observatories operate quite a lot of legacy hardware and software that would need to be updated if the current UTC definition were to be changed.
  - zajio1am 4y ago
    Because societal official/legal time is based on UTC and not on TAI. So the point is to change societal official/legal time, not just to use different time standard.