[LEAPSECS] Leap Seconds schedule prior to 1972

Tom Van Baak tvb at LeapSecond.com
Thu Apr 21 21:49:29 EDT 2016


> Hi Tom,
>
> The values presented in the 2004 Morrison and Stephenson paper are
> already smoothed using a series of cubic splines and a parabola prior
> to -700.  See their table 1 and its discussion.  The authors
> recommended simple interpolation between the listed years, so I did
> that rather than add additional smoothing.

Right. Just use their polynomial then, or go back to their original data.

> To me, the only troubling thing about creating a high-precision
> representation of low-precision data is the implication that the result
> has greater accuracy than its source.  I attempted to address that in
> my conclusion by stating that the choice of extraordinary days in
> ancient times is somewhat arbitrary.

With pUTC you're already throwing away 90% of what UTC stands for. The only thing you retain is applying a leap second just before midnight. So instead of pages of prose that describe how to do the mapping, with every century or decade different, why not just generate a function that converts JD into a proleptic leap second count. Since pUTC is fictitious anyway, there's no requirement to have the leaps at the end of a month or weirdly spaced on the 15th or 28th/29th/30th/31st. Instead just generate a leap on the day when it's needed, regardless of what day number or month number it is.

I say this because you're generating a subjective table, one based on data from a fitted polynomial, which is itself based on measurements of dubious accuracy in the first place, measurements that can be revised from time to time depending on historical research. The whole thing doesn't pass my smell test.

The other way to think about it, what are you minimizing or maximizing in the design of your tables. If someone else comes up with a different table design, how do you choose which is better. Is minimum RMS of |DUT1| the goal? Must |DUT1| < 0.9 s? How can you be sure? Can you have double leaps instead of single leaps twice a month? Must the leaps occur only at the end of a month? Why not space them every 365 / N days within a year? Then again, at this level you're dealing with JD anyway, so pUTC doesn't itself need to be tied to years, or arbitrary power of ten boundaries. Morrison and Stephenson's use of year isn't exactly strict.

Think about the code that some poor programmer is going to have to write as they read your PDF. Instead of an if-else-if sequence that goes on for pages, is there a simpler way to generate pUTC? I mean, no human is going to read your PDF and manually go through the guidelines you present. So maybe think of the code first instead of the prose.

It looks to me like you have a subjective solution looking for a poster child problem. I would feel much better if you or anyone else on the list could start with a couple of real examples of a problem, and then consider what algorithmic solutions solve the problem.

/tvb


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