IMO it's not a simple thing, even at a surface level.
"A minute has 60 seconds" is simple.
"A minute has 59, 60, or 61 seconds. Consult CGPM publications or your national timekeeping authority to find out." is not simple at all.
"A minute has 60 seconds" is simple.
"A minute has 59, 60, or 61 seconds. Consult CGPM publications or your national timekeeping authority to find out." is not simple at all.
Now, if you don’t care about the sun but about fixed intervals, you can always use TAI.
Standards are there to serve people, and we should have the choice to use the standard that fits our needs best. Changing the meaning of a standard retroactively, with no good reason and when a good alternative is available, is nothing short of irresponsible.
I think there is a good alternative available, UT1. UTC was always divergent from UT1 anyway, so this change shouldn't affect anyone who actually needs precise solar timekeeping.
More importantly, there are many good reasons to drop leap seconds, such as the massive increase in complexity they impose on all time-related code.
Standards should serve people, which is why leap seconds should never have existed. Imagine: "Sure some airliners crashed, and half the internet went offline for a couple days, but if you drive to the right longitude line, the sun will be exactly overhead at 12:00:00, and here in town it's overhead at 12:23:48. That's worth anything. I'd hate to live in a world where it was overhead at 12:23:49, or that'd be over my great-great-great grandchildren at 12:23:47."
And it has, the bound on the deviation was increased slightly to 3600 seconds
The problems with letting dUT1 > 1800 and above is that well before that it starts mattering for almost everything and then you have to consult the solution (here's just 2025's):
https://crf.usno.navy.mil/quarterly-vlbi-solution
https://www.nist.gov/pml/time-and-frequency-division/time-di...
GMT (Grenwich Mean Time) is a legacy from when Britain (and thus Grenwich, an observatory in London, England) was more important. These days GMT, even in British legislation, just means UTC. When we say "In the winter we use GMT not BST" we're not switching to or from some archaic time system, GMT is just defined as UTC+0 and BST is defined as UTC+1 the same way summer time zones work in several others places which have them.
I'm just highlighting that in most places when it says "GMT" it does not mean solar time, just like how "New Street Station" in Birmingham is not in fact a New Station, or on a New Street, it's a station which was close enough to the road in Birmingham named "New Street" that it's forever associated.
When actual Grenwich Mean Time was "still a thing" astronomers would use it for solar time because we had no better approximations. Today the IERS looks at very distant objects in the sky. We know that in some sense (relative to us) these are not moving because they're incredibly far away, and so we can use them to measure rotation. And then we adjust for where the Sun is from that data.