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

David Forbes dforbes at dakotacom.net
Thu Jul 14 12:26:20 EDT 2005


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
>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 
>>>  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 
>>  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

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