[time-nuts] Re: UTC - A Cautionary Tale

David Forbes dforbes at dakotacom.net
Thu Jul 14 11:43:25 EDT 2005

At 11:13 PM -0700 7/13/05, Rob Seaman wrote:
>>  This is a little missive from an astronomer on the delicate 
>>subject of the divergence of UTC from UTx. It seems that those 
>>bastards in the precision timing community want to abandon UTC's 
>>leap seconds entirely because they are too much trouble, and he's 
>>hopping mad.
>Note that my message was composed for astronomers, not you guys.
>Several of us in the astronomical software community have been 
>following this issue since before Y2K:
>     http://www.ucolick.org/~sla/leapsecs
>We are as "hopping mad" about the sneaky process as about the 
>proposal.  Note our two tiered objection:  they not only propose to 
>cease issuing leap seconds, they propose to continue calling the 
>resulting time scale "Coordinated Universal Time".  There are many 
>flavors of UT - UTC should not be divorced from the others.  Call a 
>leap second-less civil time anything you want - simply don't call it 

I agree that important processes should not be sneaky, but they often 
are. Manhattan Project, anyone?

>>  [His most amusing argument against modifying UTC is that astronomy 
>>software tends to use UTC not UT1 etc.]
>Amusing how?

It's amusing in that UTC is civil time, not astronomical time, which 
one would expect astronomers to use. I didn't say it's bad or wrong, 
just that it's amusing. Jokes are amusing. I have a sense of humor, 
which many people seem to lose when their favorite ideas are attacked.

>Also note that UT1 is only available after the fact.  UTC is a 
>deterministic (if segmented) timescale which provides not only an 
>approximation (and prediction) of UT1, but also provides access to 
>TAI two or three orders of magnitude more precisely yet.  It may not 
>be perfect, but then - this proposal isn't designed to provide 
>something better.  Imagine what might have been achieved if the 
>precision timing community had spent the seven year leap second 
>hiatus working to improve UTC rather than to sabotage it.

UTC is NOT deterministic. It has leap seconds inserted randomly with 
only 6 months advance notice. You can't plan a mission to Saturn 
based on UTC.

There was a big discussion about this subject on the time-nuts list a 
couple weeks ago precisely *because* UTC is not deterministic. 
Computer programmers have to stand on their heads to design systems 
to calculate future time using UTC.

>I find it surreal that it is the precision timing community who are 
>arguing that the public have no need for access to precision time.

The time the public uses doesn't need to be locked to the Earth's 
rotation to within a second over the short term. The thing to solve 
is the long-term drift, which can be predicted far in advance, but 
not to within a second a year.

I propose a better solution that will keep the civil timescale locked 
to the Earth's rotation to within a minute and be deterministic for 
hundreds of years in advance: Create leap minutes and *define them in 
advance* for the next 500 years (or however far in advance is 
practical) based on the second-order curve of the known 
characteristics of the Earth's rotation. Then the programmers will 
have an algorithm to guarantee that their clock code will work until 
long after they're dead.

>Rob Seaman
>time-nuts mailing list
>time-nuts at febo.com


--David Forbes, Tucson, AZ

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