On Aug 30, 2005, at 10:46 AM, Poul-Henning Kamp wrote:
We could replace UTC with TAI, or kill leapseconds in UTC and let
it keep its offset from TAI or do a myriad of other things and
still keep "the clock" as people see it on their wrist [1] in
sufficient sync with the light of day through minor acts of
timezone adjustments.
I challenge the use of the word "myriad" here, implying that there
are 10,000 options. The broader we allow the civil time debate to
range, the greater number of options, but many of those options are
quite distinct from any situation similar to our current vision of an
international civil time standard. I believe we will find at the end
of the day, that is, the end of an appropriate international
discussion of civil time for the third millennium, that civil time
will continue to require that the concept of the solar day be
reconciled with the concept of the second as an equal length unit of
SI time. Note that I'm not trying to drive the discussion back to
our well worn pathways - for the purposes of this message, I will
entertain the notion of a leap hour as well as the notion of a leap
second.
But, simply combining the notion of the "day" as the unit of civil
time (a "day" of whatever constant length), with the notion of a
constant interval clock (atomic or otherwise) results in significant
constraints to the search space for a solution. This would be true
even on a planet without a moon that is stealing angular momentum.
This would be true on a Earth with no historical Babylon to produce
sexigesimal notation. The constraint as you word it is to allow
corrections to correspond to "minor acts of timezone adjustments".
This is 100% equivalent to saying that a civil day must mimic a solar
day to a very narrow tolerance.
If you want to get me to agree with you on something resembling the
statement you made, then it is this:
Local Legal/Civilian time will probably always have the sun
highest in the sky somewhere around 12:00 through political
modification of timezone affiliation.
It follows trivially from there that it doesn't matter a dingos
fetid kidneys [2] to legal/civilian time what UTC does with
relation to the Sun, as long as it is not something ridiculous as
monthly leapseconds.
Again, I challenge the use of the word "trivially". And it does
matter what UTC does with relation to the Sun - even for the extremes
of the positions entertained in the original M&K article in GPS
World. Please try to move my messages out of the category of "raving
leap second supporter". I ain't talking about any of the issues that
we have previously beaten to death.
Civil Time for the 21st century will continue to mimic Mean Solar
Time. What we have been debating all this time is the meaning of the
word "mimic".
Rob Seaman
National Optical Astronomy Observatory
