Brooke,
True. However, the timescale in which Leap Hours are interesting is
also that in which 5 digit years are required, so those problems can
both be fixed by the COBOL programmers in the late 9990s. [humor]
GPS time is not a thing that astronomers want to use in the long run,
although they currently use GPS receivers to set their clocks to UTC
and derive sidereal time from that. [humorous but true]
The problem with using GPS time is that most GPS receivers convert it
to UTC before giving it to you!
At 9:03 AM -0700 7/14/05, Brooke Clarke wrote:
Hi David:
My concern is that if the time between leaps gets to be long then
there will be another Y2K type problem. I.e. programmers will
ignore the Leap Hour, figuring that they will be dead when it
occurs, and when it does there will be many broken programs.
The GPS time scale does not have leap seconds. Would it be suitable
for those applications where leap seconds are a problem?
Have Fun,
Brooke Clarke, N6GCE
--
w/Java http://www.PRC68.com
w/o Java http://www.pacificsites.com/~brooke/PRC68COM.shtml
http://www.precisionclock.com
David Forbes wrote:
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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