At 11:13 PM -0700 7/13/05, Rob Seaman wrote:
Howdy,
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
"UTC".
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
NOAO
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--
--David Forbes, Tucson, AZ
http://www.cathodecorner.com/
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