[LEAPSECS] Reliability

[Adi Stav]

Thank you for the discussion so far.

On Mon, Jan 05, 2009 at 04:31:44PM -0700, Rob Seaman wrote:

> Adi Stav wrote:

>

>> what problems could exceeding the tolerance(s) cause?

>

> Well covered in the archive.  For astronomy, 1 second of time is 15  

> seconds of arc on the equator.  This is a large error (colossal for some 

> purposes).  It doesn't appear that any other industry has actually 

> performed a coherent risk analysis.  For some reason this is asserted to 

> be the astronomers' responsibility.


Right. Well, both my memory of the archives and M. Warner Losh's summary
have uses that need to be aware of UT (actually, I think local sidereal
time, or ET in some cases, so that have to perform conversions either
way). I was referring, rather to issues with civil time having a large DUT. 

I am trying to identify a requirement for civil time having a low (say,
below 30 minutes) DUT. So far, I can think of the common legacy of legal 
time being mean solar time at some longitude, but that's about it.


>> (Especially problems that time zones far from their reference  

>> meridians, DST switches twice a year, and the difference between mean 

>> and apparent solar time don't already cause).

>

> This confuses periodic with secular effects, also in the archive.


A secural effect will eventually cause infinite DUT by definition. 
That's why I started with a question regarding a concrete bound on DUT.
Unless you mean that with any concrete bound on DUT, intercalation will
become more and more frequent? Or I miss your point again?


>> A good parallel would be adding leap hours and using the existing DST 

>> mechanism

>

> Reasons why leap hours won't work are in the archive.  There was a clear 

> consensus from both sides of the aisle that the notion of leap hours is 

> absurd.  Alternately, by relying on shifting timezones, there would be no 

> underlying stabilized civil timescale permitting commonsense timekeeping 

> inferences by humans.


I said I don't think it's a good idea necessarily, only that it is the
parallel of the Gregorian reform.

But what do you think about my suggestion of phasing the time standard 
every few centuries when the standard's DUT reaches 30 minutes? Won't it 
make leap hours workable?


>> I don't understand :)

>

> Imagine a version of the Gregorian calendar that interpolates leap days 

> only every 400 hundred years.  That would amount to about 3 months at a 

> time.  Since this is a whole season, it is equivalent to not stabilizing 

> the calendar at all.

>

> Leap hours or tweaking timezones can be interpreted the same way.  If  

> intercalary adjustments are the width of a timezone, no practical  

> stabilization is occurring.


Ah, I see. (Although, of course, half an hour or an hour in a day is much 
less harmful than a season in a year.)