[LEAPSECS] the inception of leap seconds

[Warner Losh]

On Wed, Aug 15, 2018 at 5:49 AM, Zefram <zefram at fysh.org> wrote:

> Another thing missing from the analogy is the distinction
> between arithmetical and observational calendars, which is very relevant,
> UTC being observational and the Julian calendar (the announcement's
> comparand) being arithmetical.


I wish we'd accepted a larger DUT1 variance to allow for a regular schedule
of leap seconds, even if the function changes on the scale of decades. That
would allow one to enshrine into code when the goofy things happen, making
them regular and transforming UTC into an arithmetic calendar, or at least
one that's mostly arithmetic :)

Eg, would we really be worse off if we'd said 'there will be a leap second
every 18 months starting Jan 1 1972? We're 46 years past the start, and
we'd have had 30 leap seconds with that rule, instead of the 27 leap
seconds that have been published. Sure, it's off a little, but on the
average, it's no worse than the amount we get off using the Gregorian
calendar... And this hypothetical assumes that this is how it would have
been from the start of UTC, so it would have been baked into things like
telescopes from the start...

Of course, Tom showed years ago having a different base frequency than
9,192,631,770Hz would have fit the wobble of the earth better, but that was
settled in the late 50s / early 60s so we'd have to go farther back in time
to 'fix' that. IIRC, 9,192,631,850 would have matched the millisecond per
day we're typically slow a lot better and we've had only had the need for 3
or 4 leap seconds...

We're stuck with what we have, though, and a GPS system that reads exactly
0 E/W some 100m from the actual Airy Meridian the tourists (including
recently me) pay to stand on. And yes, I know that abnormality is unrelated
to leap seconds, but it's fun to point out all the "wobbles" when you look
closely at these things...

Warner
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