[LEAPSECS] nails in the coffin of mean solar time

[Rob Seaman]

On Jun 14, 2007, at 6:06 PM, Greg Hennessy wrote:


> To codify existing practice. We don't use GMT any more, we use UTC.  

> It isn't even clear that with the closing of Greenwich observatory  

> if GMT even exits.


I didn't say GMT, I said mean solar time.  I won't belabor my  
previous arguments that civil time must closely track an underlying  
mean solar time scale.  Practice and statutes worldwide have  
identified civil time with mean solar time since the eighteenth  
century.  This is the case because it is the only logical choice for  
a civilization located on the surface of a planet (orbiting a single  
star anyway, but the "Rare Earth" hypothesis likely takes care of that).

Moving from a physical definition like "mean solar time" to a purely  
constructed time scale like "UTC as defined by ITU" is necessary - if  
you later want to pretend that mean solar time isn't the only game in  
town via the shell game of embargoing leap seconds in batches of 3600.


>> By seeking to replace mean solar time as the foundation of U.S.  

>> civil time, there is a tacit admission that UTC may subsequently  

>> not remain tied to mean solar time.

>

> Well, we *don't* use mean solar time as the foundation of US civil  

> time anymore.


Bzzzt!  See above.  The sun rises and the sun sets.  QED -  
civilization is layered on mean solar time.  It isn't a question of  
relaxing or tightening precision - it's a question of holding the  
timescale stationary wrt midnight over the lever arm of vast periods  
of time.


> Not even USNO runs transit telescopes to take sightings of the sun.


No, they use VLBI and other derived technologies.  They have gotten  
extremely good at doing this, but the ultimate goal is the same:  not  
to allow the days to drift relative to the sun in the sky.


> I consider the current situation as one where the laws don't match  

> practice, and don't see any problem with updating the laws.


If that were the intent, one might have expected some enthusiastic  
booster of rational timekeeping to mention the fact of these upcoming  
statutory improvements to online communities of similar enthusiasts  
like leapsecs, ntp, or time-nuts.  Imagine a similar statutory change  
to other wonky issues like cartographic projections, etc.  Giddy  
dweebs like us would be vibrating with barely contained excitement  
over getting a hearing in the Congress.


> To be against the proposed updates of the law on the basis that UTC  

> in the future *might* not include leap seconds seems overly  

> paranoid to me.


In a world in which it weren't patently obvious that some cabal had  
the explicit, unwavering goal of eradicating leap seconds no matter  
how astronomers might object, you would be correct.

In the world we inhabit, however, the paranoia is calibrated with  
exquisite precision.

I'll take this opportunity to make my roughly annual plea for the  
folks on the other side of the issue to actually join in the  
conversation.  Obviously you guys believe there is at least one good  
and sufficient reason to press forward with the theatrical stage show  
of embargoing leap seconds.  Care to share it with us?

With zero irony, let me say that if this is some classified DOD chain  
of reasoning that this agnostic for one sincerely prays that you know  
what the hell to do about DUT1.

Rob Seaman
NOAO