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

Mike S mikes at flatsurface.com
Tue Jul 19 09:51:28 EDT 2005

At 08:48 AM 7/19/2005, Chris O'Byrne wrote...
>Now, can you come up with a scenario extolling the virtues to the
>average person of leap seconds? Or a scenario in which an
>ever-so-slightly variable second being used by a member of the public
>proves disasterous?

Your scenario has nothing to do with calculating time intervals on an envelope, but I'll play anyway.

Assume someone chasing eclipses in the middle of the desert is an "average person," as you have. Exact same scenario, but the program was created 7 years prior to show all such events during the next century. Because of the unreliable nature of the quadratic equations which attempt to predict DUTC, the difference between UTC and UT1 is now 7 seconds (completely realistic, based on historical leap seconds).

They missed the event by 7 seconds instead of under 1. 

Had leap seconds continued as currently defined, UTC would still be sync'd to celestial events within 0.9 seconds. If the program's author used correct calculations and adequate precision, they could specify the accuracy of the results to within 1 second and that accuracy would continue for the lifetime of the program.

If this same person, who has spent many thousands of dollars in travel and equipment costs, had simply used a GPS (at minimal to no incremental cost) which gives the choice of presenting GPS time (which is parallel to TAI, and unaffected by leap seconds) and a program based on that, he would be even closer in time to that event which is 6 months away, but off considerably more in the longer term. If the programmer still desired to use UTC, it would also be possible for the program to automatically detect and adjust for the leap second, by noting the changed delta between GPS time and UTC.

(And as long as contrived scenarios are allowed, the friend in _my_ hotel room is a savant who can do UTC time intervals w/leap seconds in his head. The lead on your pencil broke.) 

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