Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Posting-Version: version B 2.10.2 9/18/84; site sdcrdcf.UUCP Path: utzoo!utcs!lsuc!pesnta!hplabs!sdcrdcf!darrelj From: darrelj@sdcrdcf.UUCP (Darrel VanBuer) Newsgroups: net.bugs,net.puzzle Subject: Re: Re: Computer bugs in the year 3200 Message-ID: <1772@sdcrdcf.UUCP> Date: Wed, 20-Feb-85 18:56:25 EST Article-I.D.: sdcrdcf.1772 Posted: Wed Feb 20 18:56:25 1985 Date-Received: Sat, 23-Feb-85 00:43:15 EST References: <246@cheviot.UUCP> <974@utastro.UUCP> <7927@brl-tgr.ARPA> <587@vu44.UUCP> <169@ur-cvsvax.UUCP> Reply-To: darrelj@sdcrdcf.UUCP (Darrel VanBuer) Distribution: net Organization: System Development Corp. R+D, Santa Monica Lines: 53 Xref: utcs net.bugs:544 net.puzzle:543 Summary: A brief history of Western calendars: as man became more civilized (and planned more details of life, and more carefully observered details of the world--a hunter gatherer really doesn't need a calendar, you just follow the seasons in what you seek out), he came to need to know as early as possible when key annual events occur (e.g. spring planting). One of the earliest techniques was instrumented observation (like Stonehenge), but this requires some considerable investment in equipment and "operators". The early Romans used a 365 day year with edicted adjustments when observation showed to much error. By the time of Julius Caesar, the measurements and understanding of the problem led to the imposition of the Julian calendar throughout the Roman empire in which every fourth year is a leap year (leaving an error of about 1 day in 125 years). By requiring a calendar which was the best science had to offer, you contribute to a smooth-running empire with everybody celebrating important religious and social days at the same time without worry that a provincial astronomer will get out of phase due to different interpretations of the observations (this was a real problem with Jewish holy days a few thousand years ago--first they had separate determination resulting in occasional missed syncronization, then signal fires from a central authority in Jerusalem which fell victim to malicious interference, and finally a computational system). Because of the residual error, by the late 16th century, Pope Gregory mandated the Gregorian calendar which combined a one-time correction of 10 days (in 1582) and the current system which omits leap years in century years not a multiple of 400. Because of religious factionalism, many areas did not change until much later (e.g. England delayed until 1752 and the Eastern Catholic churches the 20th century). There is still a residual error of about one day in 3200 years for which the necessary political solution has yet to be taken up (but based on the threshold for past action, we have about 30,000 years before it will happen :-). The official length of the year 1900 was 31,556,925.9747 seconds. The error in the actual length and change due to slowing of the Earth's rotation is such that a leap second has to be inserted every year or two by standard timekeepers such as NBS. I don't have a good handle on the error due to slowing, but I doubt we'll but up to a full day for 20,000 years yet (it's a difficult measurement because it's near the limits of current measurement technology [to clarify--that's a cumulative full day off, not a year a whole day shorter]. It may also never come due to the leap-second scheme in use by standards organizations (at least till everybody has an atomic clock and notice what the standards people are doing :-). Note that 2000 IS IS IS a leap year--ask Pope Gregory. (there has been some misinformation appearing on this point) -- Darrel J. Van Buer, PhD System Development Corp. 2500 Colorado Ave Santa Monica, CA 90406 (213)820-4111 x5449 ...{allegra,burdvax,cbosgd,hplabs,ihnp4,orstcs,sdcsvax,ucla-cs,akgua} !sdcrdcf!darrelj VANBUER@USC-ECL.ARPA