John Cowan wrote on 2005-01-23 18:37 UTC: > 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".
Why? > 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. No. A "UTC leap hour" is an inserted 60-minute repeat segment in the UTC time scale, which starts by jumping back on the UTC time scale by one hour. This has been proposed by BIPM in Torino to be done for the first time to UTC in about 2600, instead of doing the about 1800 leap seconds that would be necessary under the current |UTC - UT1| < 900 ms until then. The proposed "UTC leap hour" simply means that the definition of UTC is relaxed to (something like) |UTC - UT1| < 59 min, and the size of the adjustment leap is increased accrodingly from 1 s to 3600 s. Local civilian times are of no convern to ITU, as they are entirely the responsibility of numerous national/regional arrangements. > You seem to be using it in the sense of a 1h secular change to universal > time (lower-case generic reference is intentional). I can't understand what could be ambiguous here. A leap hour means to turn a clock forward or backward by an hour. We have done it twice a year in many LCTs. The BIPM suggested in Torino that we should do it every couple of hundred years to UTC as well, which would become permissible by going from the rule |UTC - UT1| < 900 ms to a relaxed rule such as |UTC - UT1| < 59 min. The term "leap hour" does in no way imply what time zone/scale we are talking about, and in this context we are talking mostly about UTC. [How a UTC leap hour would affect LCTs is up the maintainers of the these LCTs. Since the LTCs currently in use have their leap hours on many different days of the year, a UTC leap hour would mean that at least some LCTs would have three leap hours in that year. This could only be avoided if all LCTs would agree to do their DST leaps simultaneously with the UTC leap.] In summary: There are basically three proposals on the table: a) Keep UTC as it is (|UTC - UT1| < 900 ms) and just make TAI more widely available in time signal broadcasts b) Move from frequent UTC leap seconds to far less frequent UTC leap hours, by relaxing the UTC-UT1 tolerance (e.g., |UTC - UT1| < 59 min) c) Remove any future leap from UTC, such that UTC becomes TAI plus a fixed constant (i.e., |UTC - UT1| becomes unbounded and will start to grow quadratically). In this scenario, LCTs would have to change their UTC offset every few hundred years, to avoid day becoming night in LCTs. My views: a) is perfectly fine (perhaps not ideal, but certainly workable) b) is utterly unrealistic and therefore simply a dishonest proposal (UTC is so popular today in computing primarily because it is *free* of leap hours) c) I could live with that one, but what worries me is that it will create a long-term mess in a few millenia, when |UTC-LCT| >> 1 day. I am annoyed that this long-term mess and solutions around it are not even being discussed. (My hope would have rested on resolving the |UTC-LCT| >> 1 day problem by inserting leap days into the LCTs every few thousand years as necessary, to keep |UTC-LCT| < 36 hours this way, and that these leap days in LCTs could perhaps be the same that may be necessary anyway every few millenia to fix the remaining Easter drift in the Gregorian calendar: http://email@example.com/msg00206.html ) Markus -- Markus Kuhn, Computer Lab, Univ of Cambridge, GB http://www.cl.cam.ac.uk/~mgk25/ | __oo_O..O_oo__