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A comment on Europe pushing for lunar time zone. Parent comment

Re:Europe pushing for lunar time zone by yencabulator on Thursday March 02, 2023 @10:21AM (#34996748)
> We don't use TAI in everyday use because it's constantly and continuously changing in small ways to account for the tiny accelerations or decelerations in Earth's rotation, and that's annoying for computers. So instead we use UTC.

Wait, what? TAI is the one time standard that doesn't change. It's just a bunch of atomic clocks averaged together. As monotonic as human kind is able to manufacture, at this time.

UTC is TAI+varying offset in an effort to stay close to mean solar time.

The varying offset of UTC, called leap seconds, is what's annoying to computers. If we ran computers on TAI, they would be simpler!

And "data center time" tends to be something approximating UTC, with leap seconds smeared into continuous adjustments, just because UTC is annoying to computers.

https://en.wikipedia.org/wiki/International_Atomic_Time

https://en.wikipedia.org/wiki/Coordinated_Universal_Time

https://en.wikipedia.org/wiki/Solar_time#Mean_solar_time

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Re:Europe pushing for lunar time zone by jxf on Thursday March 02, 2023 @12:21PM (#34998683)
> Wait, what? TAI is the one time standard that doesn't change. It's just a bunch of atomic clocks averaged together. As monotonic as human kind is able to manufacture, at this time.

That is not the complete story. The calculation used to average the clocks has changed over time, thus amending TAI. The "perfect monotonic" time you're talking about is TT (terrestrial time), not TAI.

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Re:Europe pushing for lunar time zone by yencabulator on Thursday March 02, 2023 @12:42PM (#34999019)
Wikipedia about TT: "It is a theoretical ideal, and real clocks can only approximate it. [...] TT is indirectly the basis of UTC, via International Atomic Time (TAI)."

So, TAI is what we are able to measure. TT is a theoretical construct. Can't run computers on TT, can run them on TAI.

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Re:Europe pushing for lunar time zone by jxf on Thursday March 02, 2023 @12:54PM (#34999199)
Yes, I'm just saying that it's not accurate that "TAI doesn't change". It has notably and significantly changed a number of times.
[ Parent | on HN ]