On Dec 18, 2005, at 3:58 PM, Markus Kuhn wrote:
Why is it important that our clocks give a +/- 30 minutes approximation of local astronomical time?
Unimportant for some purposes. Important for others. Who ranks the relative merit? The key issue is surely a question of interoperability. As it stands now (and has for all of human history), the fundamental standard is the Earth itself (a mirror image of the Sun in the sky). This was true for local apparent time and is true for mean standard time zones. The ITU proposal would replace an extremely portable and durable and recoverable standard (as simple as measuring noon in a particular location on a given date) with a completely ad hoc relationship to some remote ensemble of hyper-technical devices. A bright middle school student could synchronize a clock against mean solar time - from first principles. On the other hand, a nobel laureate might botch the recovery of the monotonic count that is TAI should that count ever become lost.
Sure, there seem clear advantages in having midnight happen when most people are asleep, or at least outside extended business hours. So having everyone on UT is not very attractive for those living more than +/-3 hours from the prime meridian. But since most of us sleep at least 6 hours and are not (supposed to be ;-) working for at least 15 hours each day, such a simple requirement could still be achieved with just 3-5 timezones worldwide.
Sure, why not? But this is completely orthogonal to the question of the relative importance of leap seconds. No matter how wide we make the time zones, no matter how large an amplitude we allow for daylight saving/"summer" time, these are still periodic (or purely constant) effects. A leap jump - whether a second or an hour - remains a secular effect. Which is bigger? An hour per year? Or two milliseconds per century? Ill-posed question. It ain't an hour a year compared to an hour after 600 years. Spring forward AND fall back. What it is REALLY is zero hours (+1-1) per year. As small as 2 ms per 100 years is - zero per whatever is smaller. Smaller and more negligible than is the need for leap seconds.
The crudest approach would probably be a) N+S America: use local time of Cuba (~ UT - 5.5 h) b) Europe/Africa/Middle east: use local time of Poland/Greece (~ UT + 1.5 h) c) Asia + Australia: use local time of Thailand (~ UT + 6.5 h) Sure, the hours of darkness would vary substantially within each of these zones. But they do already *today* for much of the world, thanks to summer/winder. China understood this a long time ago.
I like the chutzpah of it! The pure political theater of trying to convince Washington to keep Havana time, or the serious surrealism of the Senegalese Assemblee Nationale debating the adoption of Peloponnesian Mean Time. Whatever China understands, it amounts to a constant offset, not the slope of a trend line. We aren't talking about apples and oranges, we're talking about apples and the rate of change of qumquats. In fact, it is remarkable that the existence of a significant acceleration (second derivative or quadratic effect) in the need for leap seconds is being asserted as a bogus justification for not issuing leap seconds at all. Rob Seaman National Optical Astronomy Observatory