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Re: Proposal for a new Temporal time-measurement paradigm
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From:
Brandon S. Allbery KF8NH
Date:
April 22, 2010 19:03
Subject:
Re: Proposal for a new Temporal time-measurement paradigm
Message ID:
FB36DA8D-B415-4F66-8968-5617D9400CBA@ece.cmu.edu
Minor nit:
On Apr 21, 2010, at 04:57 , Richard Hainsworth wrote:
> If a calendar system, eg., Chinese, Muslim and Jewish, defines days
> in the same way, eg., starting at midnight and incorporating leap
> seconds, for a time-zone, then the naming of the days is done by
The Jewish, Muslim, and Baha`i (and, technically at least, Christian)
religious calendars use sunset as the start of the day. Only Western
Christianity and Baha`i use the Gregorian corrections; Orthodox
Christianity and the other aforementioned calendars are Julian.
(Actually, the Baha`i calendar seems unclear on this; everything I can
find suggests that it's still an open issue for them, but for the
moment at least it's tied to the Gregorian calendar.)
The Jewish calendar doesn't recognize leap seconds; all time
measurements are variable, with the day and night separately divided
into 12 sha`ot composed of 60 dakot whose lengths vary as the length
of the day/night changes throughout the year. Sunrise and sunset are
usually defined as when the leading (resp. trailing) edge of the solar
disk crosses the horizon. (Some communities use a variation where
sunrise is considered to be "first light" and sunset the end of
twilight; *usually* these are taken as the sun being 16° below the
eastern horizon and 7.5° below the western. However, there's a lot of
variation between communities, and very little of this is fixed; one
opinion sets the start of "night" as 1 1/4 sha`ot *before* sunset!)
Islam has some other sticking points in this area: some communities
define the start of a new month based on local time, while others base
it on observations at Mecca, with the result that the calendar can
vary by a day even in the same location. (This got some discussion in
the context of Iraqi sectarian violence a few years back.)
Additionally, while Jews use a fixed calculation of when the new moon
occurs, Muslims still base the start of the month on direct
observation of the new moon, so the calendar can again be off by a day.
All of which suggests that it may not actually be possible to come up
with a mechanism suitable for representing all of these calendars.
--
brandon s. allbery [solaris,freebsd,perl,pugs,haskell] allbery@kf8nh.com
system administrator [openafs,heimdal,too many hats] allbery@ece.cmu.edu
electrical and computer engineering, carnegie mellon university KF8NH
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