On Sun 2003-07-13T23:05:16 +0100, Markus Kuhn hath writ:
> Steve Allen wrote on 2003-07-13 16:48 UTC:
> > TI without leaps turns day into night
>
> And? So does UT, for everyone sufficiently far away from Greenwich.
> That's why we have local time zones.
It should be pointed out that in the United States the statute for
time zones and the transition to and from daylight time is written
into the US Code as a fixed set of rules that are not expected to
change (and the offsets are specified with respect to GMT). This is
significantly different than countries where the annual start and end
of summer time does not happen without the issue of an decree from the
government. The problem of changing the statutory offset between
local time zones and a uniformly incrementing atomic time would be
quite different for these two types of societies.
>From the point of view of the maintainer of the timezone offset code
in a computer operating system, it is much simpler if there is a
worldwide rule for when leap hours are implemented. Of course, in the
absence of such a worldwide rule, the situation for timezone offset
code is no worse than it was for Australia during the Olympics 3 years
ago. It just seems more sensible if there were to be a central
authority recommending the year during which a leap hour would have to
be implemented.
This is the motivation for the UTH (UT accurate to one hour) in my
suggestion. UTH gives a name to a quantity that can be used in
statutes about time zones when they want to specify the offsets. UTH
does not have any properties which are interesting to the study of
earth rotation. It is merely a device which supposes that leap hours
are the least painful means of achieving the divorce between atomic
time and universal time. Yet naming and maintaining the value of the
quantity UTH recognizes explicitly that civil time will have to track
universal time over the long term. UTH is primarily a means of giving
long-standing legislation and international specifications something
that they can name when they are rewritten after a transition from
radio broadcasts of UTC to radio broadcasts of TI. Because the
initial value of DUTH is zero, use of UTH requires no immediate
rewrite, hardware, or software, or other action.
To clarify, and partly explain, what I mean
(I am using should and must as an RFC)
After a suitable interval of years has passed radio broadcast time
signals should stop inserting leap seconds and proceed from there
with no leaps whatsoever at a permanently fixed offset from TAI.
(MiniReason: Broadcasting UT has proved to be problematic in one
way or another for decades. Physical systems require uniform time
interval more than human systems require time-of-day.)
The value of the new broadcast time scale should equal the value
of UTC at the change.
(MiniReason: the transition cannot be inconsequential to all
systems, but it should be inconsequential to as many existing
systems as possible. A jump is extremely consequential.
Rest In Peace TAI.)
The new time scale must have a new name which does not imply
that it is universal time (e.g., TI).
(MiniReason: atomic time is not universal time, and time-of-day
remains a valid concept which needs an unambiguous name)
All of the above is what seems to have been agreed in Torino. In addition
The new broadcast atomic time signals must contain information
about the value of UT1 accurate to (or better than) one hour
(e.g., the DUTH value).
(MiniReason: As far as we can imagine, civil time must be
time-of-day over the long run because if it is not there will
eventually be serious calendrical problems as atomic time diverges
from universal time. Therefore some form of time-of-day must be
available *as part of the signals* in order to provide a uniform
means of establishing civil time around the world. The DUTH value
would be a recommended means for rewriting legal statutes about
time zones.)
About the above point I am adamant.
Finally, if I had my druthers (neverminding shoulds and musts)
The new broadcast time signals would contain (TI - UT1) with the
capability of microsecond precision and updates to that value
occurring almost continuously (i.e., via polynomial predictions of
its value. Initially there would be no expectation that the IERS
and the radio broadcasters could manage to provide such precision
and update rate, but eventually they could upgrade systems to
attain it.
(MiniReason: I have telescopes to point. I know that I will be
able to get the UT1 info via means other than radio time signal
broadcasts, but as long as I am wishing for the ultimate format I
would like the UT1 value to be in there. If (TI - UT1) is in
there with that precision, then time hardware manufacturers can
use it to reconstruct a UTC-like time scale for the sake of those
with legacy systems that require the old behavior. Nevertheless,
the existence of a recommended variant of UT (UTH) for civil time
would serve as a strong disincentive for local authorities to use
this high precision UT1 to create their own civil time scales.)
And I do not believe that the long term secular evolution of the solar
system is known well enough to address any changes to the Gregorian
calendar. At present there is no clear indication that any change
will be warranted before (TI - UT) has achieved a value of a full day.
--
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 Sun Jul 13 2003 - 23:08:32 PDT