On Sunday, June 22, 2003 [EMAIL PROTECTED] wrote: >I'll try to rephrase this, because it >would be good to have it in the FAQ. >If somebody can explain it better, or >more correctly, please help me!
How's this: What time scale does DateTime follow? What's up with UTC, GMT, TAI, and UT1? The DateTime modules are based on a time scale known as UTC (Coordinated Universal Time), which was adopted internationally in 1972. Before UTC, other time scales were in use, including: - GMT (Greenwich Mean Time), in which each twenty-four hour day has exactly 86,400 uniform seconds by international convention; - UT1 (Universal Time), in which day length varies, and is slowly changing, due to irregularities in the earth's rotation detected by astronomical observations (the "earth clock"); - TAI (Temps Atomique International), in which a day has 86,400 seconds whose length is derived from a chosen atomic resonance at sea level (the "atomic clock"). TAI was originally synchronized with UT1 on 1958 January 1 (i.e., on that date, UT1 - TAI = 0). UTC was developed to combine the stable atomic precision of TAI with the earth-sun accuracy of UT1. UTC is defined to differ from TAI by integer seconds and to differ from UT1 by less than .9 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>). ############# - Bruce __bruce__van_allen__santa_cruz__ca__
