[LEAPSECS] ISO Influence

[Joe Gwinn]

At 10:47 AM -0700 12/19/10, Rob Seaman wrote:

>On Dec 19, 2010, at 10:16 AM, Joe Gwinn wrote:

>

>>  There is a deep difference here:

>>

>>  In Y2K, there was going to be a discontinuity, the first 

>>occurrence of a "20xx" date in a computer world that had only known 

>>"19xx" dates.

>>

>>  By contrast, in the proposal to drop leap seconds, the periodic 

>>discontinuities would cease.

>

>There is another deep difference.  Y2K remediation involved no 

>re-imagining of our underlying concepts of calendar dates and clock 

>times.  The ITU, on the other hand, is attempting to legislate 

>reality.  Civil timekeeping is (and will remain) time-of-day.  The 

>ITU just wants UTC to lie about it.  The question is whether the 

>tolerances underlying that lie rise to an actionable level.

>

>...in addition leap seconds don't just cease - rather, DUT1-style 

>corrections will assume a growing importance.  Currently DUT1 is 

>negligible for many purposes - this won't remain the case.


In my career, I have encountered exactly one system that even knew 
what DUT1 is, and even so DUT1 was handled in application code, in 
the one place that could even understand the question.



>Leap seconds exist in service of mean solar time (sidereal time 

>adjusted to lap the Sun once annually).  Omit leap seconds and the 

>clock rate diverges from the natural rate.

>

>Discontinuities do not just cease - rather, contingent issues will 

>pop up elsewhere.  Any proposal to redefine UTC should address those 

>issues.


Well, the discontinuities are man-made.  The Earth and Stars know 
nothing of this.

In the old days, the length of the day and subsequently of the second 
was allowed to vary to accommodate natural variations in Earth 
motion.  But this was awkward for atomic clocks, so leap seconds were 
invented.

So, the issue is how and how often to match atomic timescales to 
those natural variations in Earth motion.  One can think of many 
ways, each with advantages and disadvantages.  The problem is that 
our various lists of advantages and disadvantages are not the same, 
so no single answer can work for all.

The ITU, a creature of governments, will decide on the basis of 
what's best for the larger civil society, even at the expense of the 
sciences, astronomy being especially affected.

In the broadest sense, on the national scale, it's far cheaper to 
make the astronomers to redo their handling of time than to require 
the populations to use astronomical timescales.  Not that there will 
be a line item for this rework in any national budget, but given that 
astronomy is mostly paid for by governments, all such costs must be 
in there somewhere, albeit at the expense of something else.  Like 
all government mandates.

My first job out of school was at the Federal Communications 
Commission in Washington, DC, in the 1970s.  The FCC had a similar 
public-policy issue.  Whenever anyone suggested some change in 
regulations, the immediate and universal response was that nobody has 
the money for this, so the FCC should pay, or go away.  This cycle is 
true in all regulatory agencies.

Anyway, the standard solution was to observe that radio and TV 
receivers don't last forever, and to set twelve years as the official 
economic lifetime of a receiver.  So long as the regulatory change 
was imposed twelve years in advance, no problem.  Just wait for the 
old receivers to die off.  The most recent example of this is the 
recent move to digital TV signals, and the parallel deauthorization 
of analog over-the-air broadcast to allow the spectrum to be 
re-assigned.

Joe Gwinn