[LEAPSECS] BBC radio Crowd Science

[Warner Losh]

On Tue, Jan 31, 2017 at 12:50 PM, Brooks Harris <brooks at edlmax.com> wrote:
> On 2017-01-31 02:19 PM, Warner Losh wrote:
>>
>> On Tue, Jan 31, 2017 at 12:08 PM, Steve Allen <sla at ucolick.org> wrote:
>>>
>>> On Tue 2017-01-31T13:58:15 -0500, Brooks Harris hath writ:
>>>>
>>>> Ah, so who's right?
>>>
>>> I prefer to think of a leap second as being truly intercalary.
>>> It is saying to atomic clock "It's not tomorrow yet, wait a second."
>>> It is between one calendar day of UTC and the next calendar day of UTC.
>>> It belongs to neither of them.  The tag 2016-12-31T23:59:60 is merely
>>> a way of indicating which two days it is between.
>>> It is unfortunate that nobody thought this stuff through in 1969 when
>>> the decision was made to implement the leap second, and no matter how
>>> it is expressed, encoded, and calculated it will be a special case.
>>
>> Philosophically you may be right.
>
> It doesn't seem philosophical to me. Its obviously a special case, a special
> case of interoperablity decreed by the IERS.
>>
>>
>> Mathematically, however, I don't think that makes much sense. :60 is
>> an irregular radix. It's clearly added to the prior day, just like Feb
>> 29th is part of February.
>
> Yes.
>>
>> Also, doing the long-hand math on the
>> irregular radix, it also makes sense to have it be part of the prior
>> day
>
> It is, right? And that's what Rec 460 clearly says.
>>
>> and to increment the offset at the start of the leap second.
>
> Not necessarily.
>
> What part of Gregorian YMDhms or DST makes any "sense"? They are unavoidable
> conventions, wacky unavoidable conventions with mixed radix components and
> deceptive algorithmic rules. UTC with Leap Seconds alters those conventions
> slightly. Why would we expect it to "make sense"?

"Math is hard"?

When you view it through the lens of the irregular radix that UTC time
of day is, the math falls out naturally.  The points of irregularity
are the wacky stuff. Not what to do when you have one.

> I think Bulletin C says the TAI-UTC value increments at the start of the
> day:
>
> " UTC TIME STEP on the 1st of January 2017" and
> "from 2017 January 1, 0h UTC, until further notice    : UTC-TAI = - 37s ".
>
> It doesn't say "the second before 2017 January 1".

Honestly, it isn't specific enough. It's specifying that on end of the
month a leap second is inserted. Anything beyond that is at best
informational since otherwise it would contradict TF.460. This is a
convenient shorthand, nothing more. In order for the math to work out,
the offset has to change at the start of the second.

Warner