# making leap hours workable

From: Steve Allen <sla_at_ucolick.org>
Date: Wed, 2 Jul 2003 09:49:45 -0700

On Tue 2003-07-01T20:34:58 +0100, Markus Kuhn hath writ:
[In appoximately the calendar year]
> sqrt((12 h + 84 s) / (31 s/hy^2)) * 100 + 2000 = 5736
>
> the point where International Time corresponds to local time will
> cross the International Date Line. What do we do then? Having
> International Time and local civilian time several days apart sounds
> rather unpractical for doing mental arithmetic and could lead to
> confusion far more severe than anything leap seconds might ever cause.
>
> I had briefly hoped that we can play around with 29 February and
> remove from the civilian time zones a 29 February (compared to what
> pope Gregory dictates)
[...]
> This would at first glance of course mess up the date of the spring
> equinox (the reason for the Gregorian calendar reform), and who knows
> whether people still worry about when Easter Sunday is by then.
[...]
> (Perhaps it is time to get the theologians back into this discussion
> after so many centuries ... ;-)

There's not much need to worry about the date of the equinox and
Easter for time far beyond the 58th century. The problem becomes
sociologically dire as soon as the calendar date indicated by the
atomic "TI" broadcasts differs by one day from the calendar date
indicated by "UT".

Note that the discussion that follows requires care in defining terms.

I will use UT to refer to time-of-day as measured by earth rotation
in the sense that the IAU has always meant by all forms of UT.
By extension into the future, I will use UT as meaning the calendar
which is achieved by counting those noon/midnight cycles.

I will use TI to refer to the hypothetical uniformly incrementing
broadcast atomic timescale which was named at the Torino meeting. By
extension into the future, I will use TI as meaning the calendar which
is achived by counting days of 86400 SI seconds.

As Markus pointed out, by the 58th century the calendar date as
measured by TI will become one day greater than the calendar date
measured by UT. This introduces a problem which is not soluble by
intercalary days: when it is Sunday according to TI it will still be
Saturday according to UT.

We might hypothecate that 30 centuries from now the religious
structures of today will have faded away, but that would be a risky
prediction given that the seven day week has already been entrenched
in many cultures for over 30 centuries. Plus ca change, plus c'est la
meme chose.

Depending on the nature of employment his could lead to Jews
worshipping on Friday instead of Saturday. To a muslim that really
might make TI into the "Temps Infidel" that I've mentioned before.
On the other hand, it could lead to most Christians worshipping
would feel quite vindicated from the 58th thru 84th centuries.

Basically, it seems pretty clear that in order for any change in the
scheme of broadcast time to get legislative acceptance now, it will
have to address more than just technical issues. It will have to
address this particular sociological issue. Any new scheme of
TI to be used as civil time will have to acknowledge the validity
of UT and provide means of providing UT to an acceptable accuracy.

Undoubtedly this was part of the reasoning of B. Guinot in his letter
to the director of the BIPM that led to the SRG championing leap hours.
But leap hours in TI itself patently is not an acceptable idea.
Unlike the POSIX timestamping community which has buried its head
in the sand and refused to admit that time_t should be TAI, any
form of TI must be uniformly incrementing forever.

Nevertheless, there does seem to be a way to reconcile many of
the desired notions using a kind of leap hour that permits
long term, predictable scheduling. Here is my crazier idea:

--> Define TI with some value that approximates TAI or UT now.

--> Define a new quantity UTH (Universal Time accurate to one Hour)
with a definition that ( TI - UTH ) = DUTH * 3600 SI seconds where
DUTH is a positive integer. Make a rule that DUTH can only increment
by one at Oh TI on January 1 and that changes will be announced at

--> Define the broadcast time signals for TI such that they provide
six bits for indicating the value of DUTH.

--> Work with legislatures everywhere to get them to change their
timezone and summer time legislation. In the current forms of most
legislation it is specified that the standard time zones are an
integral number of hours offset from GMT or UTC, and that summer times
are one hour ahead of that.
Get the laws changed so that they specify that standard time is an
integral number of hours offset from TI. Have them furthermore
specify that summer time begins on a particular date, but that if a
change in UTH has occurred at the beginning of a year then civil
clocks will not be incremented that year.

--> Have the IERS develop a method for providing UT1 accurate to the
microsecond for those applications that need UT better than one hour.

The important point here is that the new scheme for broadcast time
must admit the long term validity of the concept of UT and provide
it to an accuracy necessary for civil and sociological purposes.

```--
Steve Allen          UCO/Lick Observatory       Santa Cruz, CA 95064
sla_at_ucolick.org      Voice: +1 831 459 3046     http://www.ucolick.org/~sla
PGP: 1024/E46978C5   F6 78 D1 10 62 94 8F 2E    49 89 0E FE 26 B4 14 93
```
Received on Wed Jul 02 2003 - 09:50:01 PDT

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