On Thursday, July 17, 2003 Eugene van der Pijll wrote: >Bruce Van Allen schreef: >> Some may have seen the news that debate has flared up regarding the >> continued use of leap seconds. I don't know whether it will be >> resolved soon, so it seemed best to simply acknowledge the issue, and >> hope we remember to update the FAQ if something radically changes. > >This was based on a slashdot story; nevertheless it was a serious >proposal. There was a scientific meeting on the subject in Turin in May, >summarized at >http://www.mail-archive.com/[EMAIL PROTECTED]/msg00163.html (on >the LEAPSECS mailing list!). > >The options that were mentioned were: [snip] Thanks for the link. From that I gather that the issue wasn't resolved, that there is not necessarily an emerging consensus, amd that proposals for change regarding leap seconds would not be implemented for many years. I think this all means that the note about leap seconds in my draft FAQ is the best that may be said now from the DateTime standpoint. Eugene, propose something else for the FAQ if you'd like.
>> This FAQ entry gets longer every revision, but it seems important for >> acceptance of DT that we have a fairly rigorous explanation. > >I doubt it. Not many people will be interested in the precise details. >People who really need to know it (e.g. those to whom it would cost >$100,000,000 dollar if the time is out by just one second) won't be >convinced by a simple FAQ entry. (I wouldn't be, at those prices.) Well, perhaps you aren't thinking about numerous Perl programmers who work in scientific/technical fields, who have to choose some time/date module to use, and for whom DT's basis in UTC would be reassuring... >My comments below are based on my web research of a few weeks ago. I >could be wrong, but I would like to know where you got some of your >info. >From from the IERS and YOUR posts, mostly ;) I have a few responses below to your comments. In a separate message I'll post another draft, incorporating some of your suggestions. > >> ## FAQ entry: ######## >> >> UTC is widely used in scientific and technical contexts, and is >> increasingly accepted as the standard time scale for civic and >> business uses. > >"increasingly accepted"? Is there any business that is half a minute of >standard time? (Half an hour, yes. I commute by train.) >Better: "UTC (Temps Universel Coordonne, Universal Coordinated Time) is >the current standard time scale. Civil time (the time we all use in >day-to-day life) is based on UTC, and generally differs exactly an >integer number of hours from UTC, depending on your time zone." Following others' posts, I had backed off from asserting that UTC is the current standard time scale. > >> Related time scales include: >> - GMT (Greenwich Mean Time), in which each twenty-four hour day has >> exactly 86,400 uniform seconds by international convention (the >> "imperial clock"); > >AFAIK this is not true. What's not true about it? In the structure of the draft description, the main point was to establish the mathematical aspects of GMT, namely that "each twenty-four hour day has exactly 86,400 uniform seconds." Is this not the case? > >Better: "GMT (Greenwich Mean Time), the civil time in London (and by >extension, in the whole UK, and elsewhere) in winter. Since the >introduction of UTC, GMT is equal to UTC." See next FAQ version. > >> TAI was originally synchronized with UT1 on 1958 January 1 (i.e., on >> that date, UT1 - TAI = 0). To reconcile the divergence since then >> between TAI and UT1, UTC is defined to differ from TAI by integer >> atomic seconds and to differ from UT1 by less than .9 atomic seconds. > >> To maintain this relationship, leap seconds are introduced as needed >> to the UTC time scale, under the supervision of the International >> Earth Rotation and Reference Systems Service (<a >> href="http://www.iers.org/iers";>IERS</a>). > >Perhaps these paragraphs could be rewritten a bit clearer: > >TAI was originally synchronized with UT1 on 1958 January 1 (i.e., on >that date, TAI - UT1 = 0). Because of the slowing down of the rotation >of the earth, the TAI - UT1 difference has been growing since 1958. In >May 2003, TAI - UT1 was measured to be 32.4 seconds. > >UTC follows UT1 as accurately as possible, while keeping the difference >with TAI an integral number of seconds. At the time of writing, TAI - >UTC is 32 seconds. To maintain the relationship between UT1 and UTC, a >leap second will be introduced as soon as TAI - UT1 reaches 32.9 >seconds, as determined by the International Earth Rotation and Reference >Systems Service (<a href="http://www.iers.org/iers";>IERS</a>). That's not a definition, although it has some better description than I wrote. See next version. - Bruce __bruce__van_allen__santa_cruz__ca__
