[time-nuts] Re: UTC - A Cautionary Tale
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
>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:
>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.]
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.
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--David Forbes, Tucson, AZ
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