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Comment by zokier | Hacker News Reader

For practically everyone the local civil time is off from local solar time more than 30 seconds, because very few people live at the exact longitude that corresponds to their time zone. And then you got DST which throws the local time even more off.

This is ignoring the fact that due equation of time, solar noon naturally shifts around tens of minutes over the course of the year.

To drive the point, for example local mean solar time at Buckingham palace is already more than 30 seconds off from Greenwich time.

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The point is, since astronomical "time" isn't exactly on constant multiple of cesium standard seconds, and it even fluctuates due to astrophysical phenomena, applications that concern astro-kineti-geometrical reality has to use the tarnished timescale to match the motion of the planet we're on rather than following a monotonic counter pointed at a glass vial.

It is up to you to keep TAI for everything and let your representations of physical coordinates drift away into the galaxy or something, but that's not the majority choice. Overwhelming majority choose UTC time.

TAI is still nice for many high precision applications, weirdly including a lot of precisely those geo-spatial use cases, so we have both.

Sure, but that doesn't mean that we invented and practise leap seconds for the sheer fun of it.

There's very good reasons that are important behind why we try and keep UTC near UT1, so saying "it doesn't matter to anyone" without even entertaining that some people might care isn't very constructive.

Okay, I’ll bite. Who does this matter to, and why?

UTC, and leap seconds, originate from (military) navies of the world, with the intent of supporting celestial navigation. It is already dubious how useful leap seconds were for that use, and much more dubious is its use as civil timescale.

We have leap seconds to save us from having leap minutes, or leap hours.

Generally, it's useful for midnight to be at night, and midday during the day. UT1 is not regular, so you need some form of correction. Then the debate is about how big and how often.

You don't need leap minutes. Nobody cares if the sun is off by minutes, it already is anyways thanks to timezones. You don't even need leap hours. If in seven thousand years no-one has done a 1 time correction, you can just move the timezones over 1 space, like computers do all the time for political reasons.

It’s going to be multiple centuries until the cumulative leap seconds add up to 30 minutes, and by that point, a majority of the human population is likely to be living off the earth anyway.

Also, some of the most populous time zones in the world, such as the European and Chinese time zones, are multiple hours across.

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