[LEAPSECS] Reliability

[Rob Seaman]

Here's a notion I don't recall seeing before on the list:

Coordinate leap seconds with leap days.  Introduce an integral number  
of leap seconds each February 29th.  Discuss.

Adi Stav wrote:


> Then why 4 seconds? Because they could be predicted a decade in  

> advance?  Isn't that putting the cart before the horses?


Yes, indeed.  You asked a question.  I provided a guess.  Personally,  
I think the current standard is better than allowing celestial  
coordinates to slosh around by an arcminute, but it is not the  
astronomers here who have refused to dicker.


> If I reckon correctly, people on this list specified 20 or 60  

> minutes as their guesses for the limit


Some people said such things.  Why lend them greater weight than  
alternate opinions?

Nobody has specified anything.  Specifications relate to solution  
space.  We have yet to discover the requirements describing the  
problem space.  There is nothing to specify against.


> Clearly, you think DUT should be smaller. Why? For practical reasons  

> of astronomy? For other reasons?


Yes and yes.  A static geographic offset is different from introducing  
a permanent bias in the rate.  A zero-mean periodic variation as in  
the equation of time is different from a permanent bias.  Seasonal  
step function jumps are different yet again.

Embargoing leap seconds (or their equivalent) for periods of decades  
or centuries is the same as not making intercalary adjustments at  
all.  It will introduce a tilted quadratic bias in the solar rate.   
The issue isn't about offsets at all, it is about preserving the  
correct functional form of civil timekeeping.

We have heard numerous times that the Gregorian calendar is acceptable  
because the schedule is predictable.  But why is the Gregorian  
calendar desirable?

It is desirable because it stabilizes the civil calendar against the  
natural annual rhythms of life on Earth AND because it does so at a  
fine enough resolution to permit smoothing across the decades and  
centuries.  When considering dates 400 years from now - or in colonial  
America - we don't have to wonder whether April occurs before or after  
the Vernal Equinox.

Well - except for the damage visited through the delayed Gregorian  
intercalary adjustment made by the British.  Why is there an English  
butterfly called an "April Fritillary"?  Because it emerges from its  
chrysalis in March.

The clock is a subdivision of the calendar.  It needs to be stabilized  
against natural diurnal rhythms on Earth.  And the resolution has to  
be fine enough to permit useful smoothing.

Over what period of time?  That is really the heart of this whole  
discussion.  The current UTC leap second policy is sufficient.  What  
is necessary?

We stabilize the calendar every 4 years.  Why would it be considered  
reasonable to forego stabilizing the clock for a thousand years?

Rob