Comment by Dylan16807
2 days ago
> Um, because it's the prime meridian and that's how UTC is defined?
That's an explanation of how it is, not why we should care to preserve it.
The definitions of hours minutes and seconds have changed before, and in recent history.
> Which is why I was careful to specify mean solar noon.
And "mean solar noon" is meaningless to people's lives. Even in the areas where time zones do follow meridians and not country borders that are many minutes off.
> The definitions of hours minutes and seconds have changed before, and in recent history.
In terms of what physical process we use to set the standard, yes. But those very changes were made to try to preserve the same time periods that were important to humans. In other words, to not change what hours, minutes, and seconds mean intuitively to us humans as we go about our daily lives.
I completely disagree. The intuitive meaning is that a day is 24 hours and you can divide that by 60 twice. But that makes the second vary by some parts per billion, so we nailed down the second to make the technical side easier at the expense of relatability.
> The intuitive meaning is that a day is 24 hours and you can divide that by 60 twice.
And that's exactly why the SI second has the length that it has--to be as close as possible in terms of how atomic clocks work to 1/86400 of an Earth mean solar day at a chosen epoch. (Note that the actual definition before the atomic clock one was adopted was in terms of the Earth's tropical year at that epoch--but the fraction of the tropical year that was chosen was to line up the second with 1/86400 of an epoch day.) If we didn't care about "relatability", nobody would have gone to all the trouble of trying to determine how many cesium clock oscillations there were in 1/86400 of an epoch day.
> The intuitive meaning is that a day is 24 hours
Ok so far.
> and you can divide that by 60 twice
I'm not so sure. The concept of 24 hours in a day originates in civil timekeeping, yes, but not minutes and seconds. Those originally came from astronomy, and corresponded to angles, not times, and those angles are constants; they don't change as the Earth's rotation slows down or as its speed in orbit around the Sun changes over the course of a year. I don't think people's intuitive concept of minutes and seconds is that they vary according to the time of year or the tidal effects on the Earth.
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> we nailed down the second to make the technical side easier at the expense of relatability.
Would you also say that getting rid of leap seconds and allowing UTC to gradually drift away from the sun is making the technical side easier at the expense of relatability?