alt Hacker News> The complexity goes up tremendously if some condition is rarely encountered: eg leap second. This means it gets pushed to a "corner case" and tested more lightly and more rarely.
There is some talk of eliminating the leap second, which would over time have the Earth and sun diverge with regards to noon and such. One 'answer' to this concern is to have a 'leap hour' or something in the future (some future generation's problem, not ours): but given that people can't even get February 29th correct now, and it happens regularly, I don't see how a one-off event would be made to work. It'd be a huge coördination problem.
Just look at the introduction of the Gregorian calendar: it was slightly off since the time of Julius Caesar, but that minor error added up over time, to the point that to get the equinoxes/solstices back to where they 'should' be 10 days had to be removed with the Gregorian calendar. And because of politics (or a religious flavour) it took a long while for everyone to get on the same page.
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The calendar adjustments are because the planet's constant orbital period isn't a whole number of days.
The leap seconds were an attempt to have wall clock time map to the planet's rotational angle consistently despite the problem that the planet's spin varies unpredictably.
Yes the "leap hour" is a legal fiction of course. In reality in the event anybody cares about this in the distant future they will make the kind of "drastic" changes you've probably experienced twice a year for your whole life and barely noticed... More likely because the drift is so incredibly slow they won't change anything.
IMHO the correct way to handle leap seconds would have been at the same layer as timezones, i.e. a display-only thing. Timezone databases are regularly updated, you push out leap second updates there. In the worst case, people's clocks are off by one second but all the underlying timing logic doesn't crash.
Leap seconds have so many problems beyond the time adjustment. It's a small/odd enough adjustment interval that there are wildly different approaches like leap smears. On top of being so small, it's rare enough (~every 2 years), depending on how a system is used, lack of proper handling might not be obviously apparent or lack of obvious problem in one implementation ignoring it may lead to lack of care in another implementation which would have a problem ignoring it.
Leap hour replaces all of that with what is more or less equivalent to a change in DST rules (except for more time zones at once). DST changes don't go perfect either by any means... but we do them regularly enough without the world crashing down that doing an additional shift change of an extra hour every 5000 years is almost certainly less hassle and breakage than the leap second approach breaking things every ~2 years.
> There is some talk of eliminating the leap second, which would over time have the Earth and sun diverge with regards to noon and such.
<rant> It won't happen on a human scale. So why oh why do we screw around with this moronic leap-second nonsense ? Oh dear, in the year 4000 noon will arrive three minutes earlier compared to now. So? </rant>
> There is some talk of eliminating the leap second, which would over time have the Earth and sun diverge with regards to noon and such
“Over time” really glosses over how much time it would take. In 500 years there might be half as much divergence between solar noon and 12:00pm as we intentionally inflict on ourselves with DST, or that France and Spain inflicted on themselves in the 1940’s so they could share a time zone with Germany. By the time anyone will even notice we will probably change time systems for other reasons anyway. It’s not even remotely comparable to the Julian/Gregorian issue, which dealt with leap days. Each day has 86400 seconds.
If you think you're going to steal days off my life, you've got another thing coming buster!
> One 'answer' to this concern is to have a 'leap hour' or something in the future
We've had 27 leapseconds in the last 54 years [1] - an average of 0.5 seconds per year.
At that rate, solar time will drift by 60 seconds over the course of 120 years. Drifting by 10 minutes will take 1200 years.
The leap hour will be in 7200 years, around year 9226.
[1] https://en.wikipedia.org/wiki/Leap_second