[LEAPSECS] UTC Redefinition Advanced

[Jonathan E. Hardis]

On Oct 23, 2010, at 1:48 PM, Hal Murray wrote:


>

>> How many of these systems CURRENTLY properly handle leap seconds?   

>> How

>> many of these cell phones and space systems and digital devices  

>> "buried

>> beneath Antarctic ice" CURRENTLY are built to a specification that a

>> minute can contain either 59, 60, or 61 seconds?  Or that when a leap

>> second occurs, it occurs at midnight only in the UTC+0 time zone?   

>> (4:00

>> PM in the afternoon in California)

>

> Why is that such a big deal?  At worst, they reboot the system and  

> it gets

> back in sync with the loss of some data.


Okay.  At 4:00 PM PST on December 31 -- one hour before the close of  
business on the last business day of the year -- you would have folk  
on the West Coast reboot all of their financial systems, their  
communications systems, their "smart grid" electrical systems, and  
whatever else happens to sync to UTC.

Yeah, I know that we've had a lot of leap seconds over the years, and  
people have dealt with them one way or another -- mostly  
improvisationally, not following standards.  But it's becoming tougher  
and tougher to deal with.

To reiterate, my point is that people who think leap seconds are a  
good idea (and that includes me, by the way), seem to be complaining  
at the wrong end of the value chain.   Having leap seconds is  
counterproductive if they choke the infrastructure.  Take a "time  
out," on declaring leap seconds, direct the frustration towards fixing  
the infrastructure, and then some years from now have the discussion  
again on whether leap seconds would be a good idea or not.


> I think the more important issue would be calculating differences in  

> times

> that straddle a leap second.  (I'm not an astronomer.)


Here's the issue.  There's a number called "DUT1," which is the  
difference (in seconds) between UTC, an atomic time scale, and UT1, a  
solar-based time scale.  Right now, DUT1 is constrained by agreement  
to be 0.9 s, or less, in magnitude (+/-).  The proposal is to allow  
DUT1 to grow larger than 0.9 s, and that would affect systems (the few  
that care about it, mostly astronomical) that cannot handle these  
larger numbers.

Once you get over the hurdle of allowing DUT1 to be larger than 0.9,  
many additional possibilities open up.  You could concentrate the pain  
by having a "leap minute" once a century rather than a "leap second"  
every year or two.  Alternatively, you could declare leap seconds 50  
or 100 years in advance, which presumably would make their  
implementation easier and more straightforward.  Or, society could  
decide that having a leap-anything isn't worth the bother.

     - Jonathan