For the sake of the scholarship I would like to see a modification of the current text that reads As for leap seconds, we don't know the history of earth's rotation accurately enough to map SI seconds to historical solar time to more than about one-hour accuracy; see Stephenson FR (2003), Historical eclipses and Earth's rotation, A&G 44: 2.22-2.27 <http://dx.doi.org/10.1046/j.1468-4004.2003.44222.x>. A more complete reference to the accuracy of historical Delta T is in Historical values of the Earth's clock error Delta T and the calculation of eclipses Morrison, L. V. & Stephenson, F. R. Journal for the History of Astronomy (ISSN 0021-8286), Vol. 35, Part 3, No. 120, p. 327 - 336 (2004) as can be seen at http://articles.adsabs.harvard.edu/full/2004JHA....35..327M where, in particular, Table 1 gives uncertainty estimates back nearly 3000 years. For the oldest data there is an addendum Addendum: Historical values of the Earth's clock error Morrison, L. V. & Stephenson, F. R. Journal for the History of Astronomy (ISSN 0021-8286), Vol. 36, Part 3, No. 124, p. 339 (2005) http://adsabs.harvard.edu/full/2005JHA....36..339M In addition to that, for all practical purposes, civil time prior to 1972 did not use SI seconds, but rather mean solar seconds, and for dates prior to 1955 there cannot even be an argument. Therefore in the extended range of the tz database there is an arguably unspecified point when the kind of seconds counted changes from mean solar (UT) to atomic (SI). -- Steve Allen <sla@ucolick.org> WGS-84 (GPS) UCO/Lick Observatory--ISB Natural Sciences II, Room 165 Lat +36.99855 1156 High Street Voice: +1 831 459 3046 Lng -122.06015 Santa Cruz, CA 95064 http://www.ucolick.org/~sla/ Hgt +250 m
Steve Allen wrote:
In addition to that, for all practical purposes, civil time prior to 1972 did not use SI seconds, but rather mean solar seconds, and for dates prior to 1955 there cannot even be an argument. Therefore in the extended range of the tz database there is an arguably unspecified point when the kind of seconds counted changes from mean solar (UT) to atomic (SI).
The recent sample scripts were based on 'seconds', but personally all of my data is stored in a database powered by Firebird. This uses a 32 bit number for the 'date' and a 32 bit fraction for the 'part of a day' ... neatly sidesteps the leapsecond problem but is a bugger when you need DST :) Which is why we store everything in UTC and the TZ data is so critical to display 'local' time! -- Lester Caine - G8HFL ----------------------------- Contact - http://lsces.co.uk/wiki/?page=contact L.S.Caine Electronic Services - http://lsces.co.uk EnquirySolve - http://enquirysolve.com/ Model Engineers Digital Workshop - http://medw.co.uk Rainbow Digital Media - http://rainbowdigitalmedia.co.uk
Thanks, I pushed this draft of a change:
From 614b193e524d74d0b6b616b64ec1fb58aa6a3fd2 Mon Sep 17 00:00:00 2001 From: Paul Eggert <eggert@cs.ucla.edu> Date: Mon, 2 Sep 2013 01:51:15 -0700 Subject: [PATCH] * Theory: Improve citation to Morrison & Stephenson.
Mention the 1972 UTC transition. See Steve Allen in <http://mm.icann.org/pipermail/tz/2013-September/019770.html>. --- Theory | 16 ++++++++++------ 1 file changed, 10 insertions(+), 6 deletions(-) diff --git a/Theory b/Theory index 4081b24..bd62c5c 100644 --- a/Theory +++ b/Theory @@ -240,12 +240,16 @@ locations differ in LMT. Historically, not only did different locations in the same zone typically use different LMT offsets, often different people in the same location maintained mean-time clocks that differed significantly, many people used solar or some other time -instead of mean time, and standard time often replaced LMT only gradually -at each location. As for leap seconds, we don't know the history -of earth's rotation accurately enough to map SI seconds to historical -solar time to more than about one-hour accuracy; see Stephenson FR -(2003), Historical eclipses and Earth's rotation, A&G 44: 2.22-2.27 -<http://dx.doi.org/10.1046/j.1468-4004.2003.44222.x>. +instead of mean time, and standard time often replaced LMT only +gradually at each location. As for leap seconds, civil time was not +based on atomic time before 1972, and we don't know the history of +earth's rotation accurately enough to map SI seconds to historical +solar time to more than about one-hour accuracy. See: Morrison LV, +Stephenson FR. Historical values of the Earth's clock error Delta T +and the calculation of eclipses. J Hist Astron. 2004;35:327-36 +<http://adsabs.harvard.edu/full/2004JHA....35..327M>; Historical +values of the Earth's clock error. J Hist Astron. 2005;36:339 +<http://adsabs.harvard.edu/full/2005JHA....36..339M>. As noted in the README file, the tz database is not authoritative (particularly not for pre-1970 time stamps), and it surely has errors. -- 1.8.1.2
participants (3)
-
Lester Caine -
Paul Eggert -
Steve Allen