4 ms·

Might be a dumb question, but these leap seconds seem like they cause way more hassle than they are worth. Why don't we just stop adding them?

paxys 5y ago
They cause a hassle but are required. The Earth's rotation isn't perfectly constant, so without any adjustment we would keep drifting away from solar time.
- neckardt 5y ago
  What's the problem with slowly drifting away from solar time? If 9:00am became 9:10am by the time I'm 100 years old I don't think I'd encounter any difficulties. Who requires this level of accuracy?
  - beerandt 5y ago
    Because then you'd still need an almanac of the drift in determining celestial location/navigation. It's easier to just keep high noon at the Greenwich observatory as the defining datum, since most worldwide coordinates ultimately reference back to it, being 0deg longitude. Ultimately, either time or location would need to be adjusted, and it's easier to do time. Plus it's consistent with what's been done historically.
  - gh02t 5y ago
    There isn't a huge problem with changing it, there are people who want to do exactly that and do something else instead. The prominent alternatives that I know of still do something to keep time tied to the mean solar day, though, and changing time standards can be a complicated process so it's likely to take a while. https://en.wikipedia.org/wiki/Leap_second#International_proposals_for_elimination_of_leap_seconds https://en.wikipedia.org/wiki/Leap_second#International_prop...
  - IfOnlyYouKnew 5y ago
    It’s sorta like asking why we don’t fix pi at 3.1, even if the scale may (initially) be smaller. Or get rid of time zones: It’s sacrificing truth for the convenience of about a dozen people in IT.
    - tablespoon 5y ago
      > It’s sacrificing truth for the convenience of about a dozen people in IT. But those dozen IT people think the trade off is really worth it (for them)!
    - Gigachad 5y ago
      This is exactly the kind of thing that is often done. Some software will just treat all months as having 30 days because it simplifies logic massively and doesn't cause that much of an issue.
    - MiddleEndian 5y ago
      >It’s sacrificing truth for the convenience of about a dozen people in IT. And this kind of thing can never be undone. See: NTSC "60" Hz actually being 59.94 Hz due to the transition between black and white and color TV. Monitors today still have this lasting effect for consistency's sake.
- himinlomax 5y ago
  They are not required when using TAI. The only sensible way to count time is with TAI. UTC and its leap seconds should only be used for display/parsing, not for counting time. That people do otherwise is rage inducing.
  - nextaccountic 5y ago
    YEP! no timestamp should EVER be in UTC.
  - user-the-name 5y ago
    A time expressed in TAI that is in the future has no conversion to human-readable time. That is not a very useful piece of data for many, many use cases.
    - d110af5ccf 5y ago
      > TAI that is in the future has no conversion to human-readable time Doesn't it convert to within some margin for error? Checking Wikipedia, I see that the delta between TAI and Unix time has only drifted 27 seconds since 1972. That should be more than sufficient for your average mundane human readable purpose.
beerandt 5y ago
For navigation especially, these leap seconds are important so that celestial bodies rise/set/transit overhead at the expected times when calculating longitude. Lots of critical military devices still use star based navigation, and likely even more will in the future, since it's become obvious we can't rely on NAVSTAR GPS to be working if we go to war.
- toomuchtodo 5y ago
  > Lots of critical military devices still use star based navigation, and likely even more will in the future, since it's become obvious we can't rely on NAVSTAR GPS to be working if we go to war. I pine for a commercial/hobbyist grade celestial navigation system (point CCD at sky, get position). If anyone has any recommendations or pointers, would love them.
  - kadoban 5y ago
    You still need an accurate clock even if you can use a view of the sky, right? Not sure the best way that could work. Could accept optional updates to time via GPS? Would this potentially work during the day, or do you need to be able to see stars? If you can see the Sun I guess that should be good enough, if the sensor can even handle that without clipping to hell? Do you also have to be able to accurately measure angle to the horizon too? I'm not all that familiar with celestial navigation in practice.
    - toomuchtodo 5y ago
      So most of my research is historical (military hardware [1]) and amateur. Building my own attempt has been on my TODO list for sometime. Assume I would use something like a CSAC (chip scale atomic clock) for local high accuracy, high stability timekeeping (and for my purposes, it's probably okay to cheat and fallback to GPS to get a PPS time update occasionally). It's my understanding that existing celestial navigation systems can discern stars even during daylight, but as I mentioned, I haven't tried it yet (although when you can detect celestial markers, accuracy can be as good as ~20 meters with a fix provided in sub 30 seconds based on state of the art). To me, there's something profound about the idea of locating yourself in 3D space using light from stars light years away. GPS is great, but the universe is inherently providing beacons (not just stars, but also pulsars [2]) for positioning and guidance. That's very cool! [1] https://timeandnavigation.si.edu/multimedia-asset/nortronics-nas-14v2-astroinertial-navigation-system https://timeandnavigation.si.edu/multimedia-asset/nortronics... (Nortronics NAS-14V2 Astroinertial Navigation System: Mounted behind the SR-71’s cockpit, this unit, affectionately known as “R2-D2,” computed navigational fixes using stars sighted through the lens in the top of the unit. These fixes were used to update the inertial navigation system and provided course guidance with an accuracy of at least 90 meters (300 feet). Some current aircraft and missile systems use improved versions as a backup to GPS.") [2] https://directory.eoportal.org/web/eoportal/satellite-missions/content/-/article/iss-utilization-nicer-sexta-1 https://directory.eoportal.org/web/eoportal/satellite-missio... (ISS Utilization: NICER/SEXTANT) (I have not acquired nor reversed engineering any military grade celestial navigation equipment or systems, please don't sic ITAR on me)

paxys 5y ago

They cause a hassle but are required. The Earth's rotation isn't perfectly constant, so without any adjustment we would keep drifting away from solar time.

neckardt 5y ago
What's the problem with slowly drifting away from solar time? If 9:00am became 9:10am by the time I'm 100 years old I don't think I'd encounter any difficulties. Who requires this level of accuracy?
- beerandt 5y ago
  Because then you'd still need an almanac of the drift in determining celestial location/navigation. It's easier to just keep high noon at the Greenwich observatory as the defining datum, since most worldwide coordinates ultimately reference back to it, being 0deg longitude. Ultimately, either time or location would need to be adjusted, and it's easier to do time. Plus it's consistent with what's been done historically.
- gh02t 5y ago
  There isn't a huge problem with changing it, there are people who want to do exactly that and do something else instead. The prominent alternatives that I know of still do something to keep time tied to the mean solar day, though, and changing time standards can be a complicated process so it's likely to take a while. https://en.wikipedia.org/wiki/Leap_second#International_proposals_for_elimination_of_leap_seconds https://en.wikipedia.org/wiki/Leap_second#International_prop...
- IfOnlyYouKnew 5y ago
  It’s sorta like asking why we don’t fix pi at 3.1, even if the scale may (initially) be smaller. Or get rid of time zones: It’s sacrificing truth for the convenience of about a dozen people in IT.
  - tablespoon 5y ago
    > It’s sacrificing truth for the convenience of about a dozen people in IT. But those dozen IT people think the trade off is really worth it (for them)!
  - Gigachad 5y ago
    This is exactly the kind of thing that is often done. Some software will just treat all months as having 30 days because it simplifies logic massively and doesn't cause that much of an issue.
  - MiddleEndian 5y ago
    >It’s sacrificing truth for the convenience of about a dozen people in IT. And this kind of thing can never be undone. See: NTSC "60" Hz actually being 59.94 Hz due to the transition between black and white and color TV. Monitors today still have this lasting effect for consistency's sake.
himinlomax 5y ago
They are not required when using TAI. The only sensible way to count time is with TAI. UTC and its leap seconds should only be used for display/parsing, not for counting time. That people do otherwise is rage inducing.
- nextaccountic 5y ago
  YEP! no timestamp should EVER be in UTC.
- user-the-name 5y ago
  A time expressed in TAI that is in the future has no conversion to human-readable time. That is not a very useful piece of data for many, many use cases.
  - d110af5ccf 5y ago
    > TAI that is in the future has no conversion to human-readable time Doesn't it convert to within some margin for error? Checking Wikipedia, I see that the delta between TAI and Unix time has only drifted 27 seconds since 1972. That should be more than sufficient for your average mundane human readable purpose.

beerandt 5y ago

For navigation especially, these leap seconds are important so that celestial bodies rise/set/transit overhead at the expected times when calculating longitude. Lots of critical military devices still use star based navigation, and likely even more will in the future, since it's become obvious we can't rely on NAVSTAR GPS to be working if we go to war.

toomuchtodo 5y ago
> Lots of critical military devices still use star based navigation, and likely even more will in the future, since it's become obvious we can't rely on NAVSTAR GPS to be working if we go to war. I pine for a commercial/hobbyist grade celestial navigation system (point CCD at sky, get position). If anyone has any recommendations or pointers, would love them.
- kadoban 5y ago
  You still need an accurate clock even if you can use a view of the sky, right? Not sure the best way that could work. Could accept optional updates to time via GPS? Would this potentially work during the day, or do you need to be able to see stars? If you can see the Sun I guess that should be good enough, if the sensor can even handle that without clipping to hell? Do you also have to be able to accurately measure angle to the horizon too? I'm not all that familiar with celestial navigation in practice.
  - toomuchtodo 5y ago
    So most of my research is historical (military hardware [1]) and amateur. Building my own attempt has been on my TODO list for sometime. Assume I would use something like a CSAC (chip scale atomic clock) for local high accuracy, high stability timekeeping (and for my purposes, it's probably okay to cheat and fallback to GPS to get a PPS time update occasionally). It's my understanding that existing celestial navigation systems can discern stars even during daylight, but as I mentioned, I haven't tried it yet (although when you can detect celestial markers, accuracy can be as good as ~20 meters with a fix provided in sub 30 seconds based on state of the art). To me, there's something profound about the idea of locating yourself in 3D space using light from stars light years away. GPS is great, but the universe is inherently providing beacons (not just stars, but also pulsars [2]) for positioning and guidance. That's very cool! [1] https://timeandnavigation.si.edu/multimedia-asset/nortronics-nas-14v2-astroinertial-navigation-system https://timeandnavigation.si.edu/multimedia-asset/nortronics... (Nortronics NAS-14V2 Astroinertial Navigation System: Mounted behind the SR-71’s cockpit, this unit, affectionately known as “R2-D2,” computed navigational fixes using stars sighted through the lens in the top of the unit. These fixes were used to update the inertial navigation system and provided course guidance with an accuracy of at least 90 meters (300 feet). Some current aircraft and missile systems use improved versions as a backup to GPS.") [2] https://directory.eoportal.org/web/eoportal/satellite-missions/content/-/article/iss-utilization-nicer-sexta-1 https://directory.eoportal.org/web/eoportal/satellite-missio... (ISS Utilization: NICER/SEXTANT) (I have not acquired nor reversed engineering any military grade celestial navigation equipment or systems, please don't sic ITAR on me)