[LEAPSECS] Cost: getting rid of GMT & discontinuing leap seconds

Rob Seaman seaman at noao.edu
Mon Oct 25 10:53:28 EDT 2010

On Oct 25, 2010, at 12:01 AM, Brian Garrett wrote:

> More accurately, civil timekeeping is sorta kinda like mean solar time. For now.

See numerous (perhaps beyond count) threads from the archives.

One more time. The entire reason that the ITU-R scheme can be contemplated is that the SI "second" (what should have been called the "essen") was mistakenly sized "sorta kinda like" the Babylonian second (1/60 of 1/60 of 1/24 of a day). Sure the ITU-R can cheat for a while for some purposes, but this is only because for that period for those purposes an "SI day" (a non-existent unit) is close enough to resemble the actual mean solar day (a unit predating mathematics). Interval time shouldn't even be represented with sexagesimals (a way of expressing angles).

Etc and so forth.

> There's no reason that couldn't change. If legislators were somehow to be convinced that TAI or GPS time were the way to go, then that's what they'd impose and that's what _hoi polloi_ would use.

Legislators can attempt to impose all sorts of things. Over the long term, the true underlying natural "requirements" (in the engineering sense) will reveal themselves.

Another name for "hoi polloi" is "citizens" or "customers".

> Indeed, I can totally imagine how that could happen, especially since they already think imposing an offset of 216000 seconds for seven months out of the year is a good idea.

Confuses periodic and secular effects. Apparent solar time is a red herring. Mean solar time is simply the natural sidereal period of the Earth adjusted for one day "lost" each year lapping the Sun.

Have no idea what the number 216000 seconds (2.5 days) is supposed to mean.

> Anybody who uses UTC professionally and does not live in a place where UTC is the local zone time has already divorced themselves from local mean solar time. So has any location that uses summer/daylight saving time.

UTC is the zero point for the entire standard zone civil timekeeping system. It is one unified whole. It is the existence of an underlying common timescale that permits separate time zones and variations like daylight saving time to function.


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