I like it!
Barring any complaints I will happily put it up. (Maybe with a test
case that exposes a leap second so that if the handling changes we
will rememer to change the text).
-ben
On Thu, Jul 17, 2003 at 10:03:13AM -0700, Bruce Van Allen wrote:
> Hi All:
>
> Here's a second revised FAQ covering DateTime's use of the UTC time scale. If this
> is OK (Dave and Flavio?), Ben, could you add it to the DT FAQ?
>
> 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 FAQ entry gets longer every revision, but it seems important for acceptance of
> DT that we have a fairly rigorous explanation.
>
> ## FAQ entry: ########
>
> 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 established internationally in 1972.
>
> UTC is widely used in scientific and technical contexts, and is increasingly
> accepted as the standard time scale for civic and business uses.
>
> 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");
>
> - 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").
>
> UTC was developed to combine the stable atomic precision of TAI with the earth-sun
> accuracy of UT1.
>
> 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>).
>
> The DateTime modules account for UTC leap seconds, providing full conformance with
> UTC.
>
> NOTE: As of 2003, there was discussion about UTC's future use of leap seconds. In
> the event of a change in the UTC definition, the most likely outcome is that the
> DateTime modules will continue to follow UTC, and any leap seconds already
> introduced will be preserved.
>
> ## End of FAQ entry #####
>
> - Bruce
>
> __bruce__van_allen__santa_cruz__ca__
