Re: Time after Time
Poul-Henning Kamp wrote on 2005-01-23 09:00 UTC: any leap hours that prevented this would, if ever implemented, be even more traumatic than leap seconds are now. they already happen here twice a year, and by now even Microsoft has gotten it right. OBJECTION, your Time Lords! UTC currently certainly has *no* two 1-h leaps every year. What the witness tries here is merely a poor attept to confuse the jury. He muddles the distinction between local civilian time, which we all know is entirely subject to our politicians deep-seated desires to manipulate us into getting out of bed earlier in summer, and UTC, which is what all modern computers use internally for time keeping today, below the user interface, where a 1-h leap is entirely unprecedented and uncalled for. [By the way, and for the record, may I remind the jury that the quoted Microsoft *is* actually the one large operating-system vendor who still has not quite yet gotten it right, as all Windows variants still insist on approximating in the PC BIOS clock LCT instead of UTC. Rebooting during the repeat hour after DST *will* corrupt your PC's clock. Gory details: http:// www.cl.cam.ac.uk/~mgk25/mswish/ut-rtc.html ] In addition to being historically unprecedented, such a move would be illegal in the United States and some other countries, which have laws explicitly defining their time zones based on solar mean time, unless such laws were changed. The laws, wisely, do not say how close to solar mean time, and parts of USA already have offsets close to or exceeding one hour anyway. As Ron Beard said wisely in his opening address in Torino, laws can be changed fairly easily, and this discussion should certainly not be about reinterpreting *past* legislation. Instead, it should be entirely about making a scientific, technical, and practical recommendation for *future* legislation. If you read, just one example, to deviate a bit from the overwhelmingly US/UK-centricism of this legal argument, the relevant German legislation, http://www.cl.cam.ac.uk/~mgk25/time/zeitgesetz.en.html then you will find that it consists at the moment simply of a pretty exact technical description of UTC. In other words, it follows exactly the relevant ITU recommendation! If the ITU recommendation were changed, for a good cause and with wide international consensus, I have little doubt that the German parliament and pretty much every other parliament would be sympathetic and update the national legislation accordingly. German laws are already updated almost each time the BIPM revises some aspect of the SI. Countries update their national radio interference and spectrum management legislation regularly based on the international consensus that is being negotiated within the ITU. The US and UK are actually no different from that, except that the subtle differences between GMT and UTC have escaped political attention in these two countries so far, and as a result, they still have a technically rather vague definition of time in their law books, and leave in practice all the details up to the Time Geeks as USNO, NPL, etc. If you think that discussions within the ITU should feel constrained by the legislation of individual member countries, as opposed to setting guidelines for future legislation there, then you have simply misunderstood the entire purpose of the process. Markus -- Markus Kuhn, Computer Lab, Univ of Cambridge, GB http://www.cl.cam.ac.uk/~mgk25/ | __oo_O..O_oo__
Re: Time after Time
Markus Kuhn scripsit: UTC currently certainly has *no* two 1-h leaps every year. There seems to be persistent confusion on what is meant by the term leap hour. I understand it as a secular change to the various LCT offsets, made either all at once (on 1 Jan 2600, say) or on an ad-lib basis. You seem to be using it in the sense of a 1h secular change to universal time (lower-case generic reference is intentional). Can anyone quote chapter and verse from Torino to show exactly what was meant? Or is the text in fact ambiguous? If you read, just one example, to deviate a bit from the overwhelmingly US/UK-centricism of this legal argument, I keep talking about the Chinese example. Consider the city of Kashi, population about 175,000. Its longitude is about 76 E, which means that its LMT is about GMT+5. Its LCT, however, is Asia/Shanghai, or UTC+8. If all those people can live with an LCT that is three hours away from the sun, we can stand rather lower discrepancies just fine. -- Don't be so humble. You're not that great. John Cowan --Golda Meir[EMAIL PROTECTED]
Re: two world clocks AND Time after Time
On Thu 2005-01-20T14:59:18 -0700, Rob Seaman hath writ: Leap seconds are a perfectly workable mechanism. Systems that don't need time-of-day should use TAI. Systems that do need time-of-day often benefit from the 0.9s approximation to UT1 that UTC currently provides. Let's stop pretending that *both* atomic time and time-of-day are not needed. Instead, let's direct our efforts toward implementing improved systems for conveying both of these fundamental timescales to users of both precision and civil time. On Sat 2005-01-22T20:43:51 -0500, Daniel R. Tobias hath writ: Now, if a time standard is to be defined based solely on constant SI seconds, with no reference to astronomy, then why even include all the irregularities of the Gregorian Calendar, with its leap year schedule designed to keep in sync with the Earth's revolutions? It really makes no sense that TAI includes days, years, and so on at all, and this will seem particularly senseless when the current date by TAI is a day or more removed from Earth-rotational time, as will happen in a few millennia. What is really needed is two different time standards: a fixed- interval standard consisting solely of a count of SI seconds since an epoch (no need for minutes, hours, days, months, and years), and a civil-time standard that attempts, as best as is practical, to track the (slightly uneven) motions of the Earth. Of course there are other units of time in civil history which have been converted from actual representations into conventional ones. Sailors have no qualms about calling out the next high tide in terms of local civil time (now practically based on UTC). They all know that the times shift by around an hour every day. The month lost its connection with the moon early in the Roman era. Everybody knows, and in general nobody cares, that the moon is not new at the beginning of a month in the Gregorian calendar. The Gregorian year is pretty good, but three millenia hence the vernal equinox will have drifted discernably from the original intent. In general nobody cares about the date of Easter that much, and (as seen in Duncan Steel's book) even some of the best astronomers have not understood the distinction between the tropical year (as popularly defined by Newcomb) and the Vernal Equinox Year that Pope Gregory's calendar actually aimed to match. Above Rob Seaman and Danial Tobias have echoed some of the issues discussed by Essen himself in his autobiographical work Time for Reflection which his son-in-law has reproduced at http://www.btinternet.com/~time.lord/ In particular, this footnote http://www.btinternet.com/~time.lord/TheAtomicClock.htm#_msocom_1 (and the entire chapter containing it) reveals that the tension between the physicists and the astronomers (notably Stoyko, who has largely been written out of history) was great enough that there almost became two SI units for time, one being the second based on the day, and one being the Essen based on the cesium resonance. But Essen claims for himself (in both this autobiography and in Metrologia http://www.bipm.org/metrologia/ViewArticle.jsp?VOLUME=4PAGE=161-165 ) the credit for recognizing that the existing systems of time distribution (and now presumably extended to time computation) basically cannot be expected to tolerate the existence of two kinds of time. I don't think this is really true anymore, but it is admittedly costly. It was the astronomers who first made the mistake of counting a truly uniform time scale using the calendrical/sexagesimal notation originally based on earth rotations (and now concisely communicated using ISO 8601). It was the physicists who pushed to continue the practice. Knowing the tides is a specialist operation, and has always been. Knowing the phase of the moon is a specialist operation, and has been in western culture for over two millenia. What we are being told by the Time Lords is that, starting from a date in the near future, knowing when noon is will also be a specialist operation. Month is entirely conventional in its meaning. Year is entirely conventional in its meaning. So soon day will be entirely conventional in its meaning. All of them become predictable, albeit upon examination silly, extensions of things which originally meant something else. The priesthood of astronomy has become irrelevant to the general populace, and the priesthood of the physicists has taken precedence. The trick will be to educate the general public that 12:00 means slightly less about where the sun is in longitude than the Gregorian calendar date means about where the sun is in latitude. Both of these schemes fail, it's just that atomic time fails by a full hour within 1000 or so years whereas the Gregorian calendar fails by a full day only after another 2000 or so years. I really like sundials, mean solar time, and the analemma. I think it is disingenuous to use the methods we see being used by the atomic clock keepers to
