If I may step in this discussion, I agree that we shall stick to mean solar time as the one and only logical time scale. But, UTC with leap hours would still be a realization of mean solar time. The solar time at the very same legal time varies by +/- 30 minutes within a given time zone. Moreover, as we all know, the eccentricity and the declination of the equator on the ecliptic induce variations of the true solar time of +/- 15 minutes. So I don't understand this assertion that replacing leap seconds by leap hours would break any link to mean solar time ...
Jerome Delporte. CNES - French Space Agency. -----Message d'origine----- De : [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] De la part de Rob Seaman Envoyé : vendredi 15 juin 2007 10:30 À : Leap Second Discussion List Objet : Re: [LEAPSECS] nails in the coffin of mean solar time On Jun 14, 2007, at 6:06 PM, Greg Hennessy wrote: > To codify existing practice. We don't use GMT any more, we use UTC. > It isn't even clear that with the closing of Greenwich observatory > if GMT even exits. I didn't say GMT, I said mean solar time. I won't belabor my previous arguments that civil time must closely track an underlying mean solar time scale. Practice and statutes worldwide have identified civil time with mean solar time since the eighteenth century. This is the case because it is the only logical choice for a civilization located on the surface of a planet (orbiting a single star anyway, but the "Rare Earth" hypothesis likely takes care of that). Moving from a physical definition like "mean solar time" to a purely constructed time scale like "UTC as defined by ITU" is necessary - if you later want to pretend that mean solar time isn't the only game in town via the shell game of embargoing leap seconds in batches of 3600. >> By seeking to replace mean solar time as the foundation of U.S. >> civil time, there is a tacit admission that UTC may subsequently >> not remain tied to mean solar time. > > Well, we *don't* use mean solar time as the foundation of US civil > time anymore. Bzzzt! See above. The sun rises and the sun sets. QED - civilization is layered on mean solar time. It isn't a question of relaxing or tightening precision - it's a question of holding the timescale stationary wrt midnight over the lever arm of vast periods of time. > Not even USNO runs transit telescopes to take sightings of the sun. No, they use VLBI and other derived technologies. They have gotten extremely good at doing this, but the ultimate goal is the same: not to allow the days to drift relative to the sun in the sky. > I consider the current situation as one where the laws don't match > practice, and don't see any problem with updating the laws. If that were the intent, one might have expected some enthusiastic booster of rational timekeeping to mention the fact of these upcoming statutory improvements to online communities of similar enthusiasts like leapsecs, ntp, or time-nuts. Imagine a similar statutory change to other wonky issues like cartographic projections, etc. Giddy dweebs like us would be vibrating with barely contained excitement over getting a hearing in the Congress. > To be against the proposed updates of the law on the basis that UTC > in the future *might* not include leap seconds seems overly > paranoid to me. In a world in which it weren't patently obvious that some cabal had the explicit, unwavering goal of eradicating leap seconds no matter how astronomers might object, you would be correct. In the world we inhabit, however, the paranoia is calibrated with exquisite precision. I'll take this opportunity to make my roughly annual plea for the folks on the other side of the issue to actually join in the conversation. Obviously you guys believe there is at least one good and sufficient reason to press forward with the theatrical stage show of embargoing leap seconds. Care to share it with us? With zero irony, let me say that if this is some classified DOD chain of reasoning that this agnostic for one sincerely prays that you know what the hell to do about DUT1. Rob Seaman NOAO _______________________________________________ LEAPSECS mailing list LEAPSECS@leapsecond.com http://six.pairlist.net/mailman/listinfo/leapsecs _______________________________________________ LEAPSECS mailing list LEAPSECS@leapsecond.com http://six.pairlist.net/mailman/listinfo/leapsecs
