[PROPOSED] Cite Rec. ITU-R TF.460-6 for leap seconds
(Inspired by patch proposed by Chris Woodbury.) * leapseconds.awk (BEGIN): * tz-link.html (Precision timekeeping): Add ITU-R citation. * leapseconds.awk (BEGIN): Drop mention of rolling leap seconds, as the ITU-R doesn’t mention them and this script doesn’t generate them. --- leapseconds.awk | 16 +++++++++------- tz-link.html | 4 ++++ 2 files changed, 13 insertions(+), 7 deletions(-) mode change 100644 => 100755 leapseconds.awk diff --git a/leapseconds.awk b/leapseconds.awk old mode 100644 new mode 100755 index 242e9d6..241da92 --- a/leapseconds.awk +++ b/leapseconds.awk @@ -16,6 +16,11 @@ BEGIN { print "# The NTP Timescale and Leap Seconds" print "# <https://www.eecis.udel.edu/~mills/leap.html>." print "" + print "# The rules for leap seconds are specified in Annex 1 (Time scales) of:" + print "# Standard-frequency and time-signal emissions." + print "# International Telecommunication Union - Radiocommunication Sector" + print "# (ITU-R) Recommendation TF.460-6 (02/2002)" + print "# <https://www.itu.int/rec/R-REC-TF.460-6-200202-I/>." print "# The International Earth Rotation and Reference Systems Service" print "# periodically uses leap seconds to keep UTC to within 0.9 s of UT1" print "# (which measures the true angular orientation of the earth in space)" @@ -29,15 +34,12 @@ BEGIN { print "# accounting for the discrepancy between atomic time and the earth's rotation" print "# did not exist. The first (\"1 Jan 1972\") data line in leap-seconds.list" print "# does not denote a leap second; it denotes the start of the current definition" - print"# of UTC." + print "# of UTC." print "" print "# The correction (+ or -) is made at the given time, so lines" - print "# will typically look like:" - print "# Leap YEAR MON DAY 23:59:60 + R/S" - print "# or" - print "# Leap YEAR MON DAY 23:59:59 - R/S" - print "" - print "# If the leap second is Rolling (R) the given time is local time (unused here)." + print "# typically look like this:" + print "# Leap YEAR MON DAY 23:59:60 + S" + print "# A negative leap second's columns 5 and 6 would be '23:59:59' and '-'." monthabbr[ 1] = "Jan" monthabbr[ 2] = "Feb" diff --git a/tz-link.html b/tz-link.html index 85fc001..234c04e 100644 --- a/tz-link.html +++ b/tz-link.html @@ -929,6 +929,10 @@ scales used by each landed mission on Mars.</li> dedicated not only to leap seconds but to precise time and frequency in general. It covers the state of the art in amateur timekeeping, and how the art has progressed over the past few decades.</li> +<li>The rules for leap seconds are specified in Annex 1 (Time scales) of <a +href="https://www.itu.int/rec/R-REC-TF.460-6-200202-I/">Standard-frequency +and time-signal emissions</a>, International Telecommunication Union – +Radiocommunication Sector (ITU-R) Recommendation TF.460-6 (02/2002).</li> <li><a href="https://www.iers.org/IERS/EN/Publications/Bulletins/bulletins.html"><abbr title="International Earth Rotation and Reference Systems Service">IERS</abbr> -- 2.17.1
On Thu 2019-07-04T00:35:32-0700 Paul Eggert hath writ:
Subject: [tz] [PROPOSED] Cite Rec. ITU-R TF.460-6 for leap seconds
In addition to the listed changes I suggest being more specific about the meaning of UT1 in leapseconds.awk by defining what is meant by "space".
print "# The International Earth Rotation and Reference Systems Service" print "# periodically uses leap seconds to keep UTC to within 0.9 s of UT1" print "# (which measures the true angular orientation of the earth in space)"
to
print "# The International Earth Rotation and Reference Systems Service" print "# periodically uses leap seconds to keep UTC to within 0.9 s of UT1" print "# (which is a measure of the angular orientation of the earth's crust" print "# with respect to a reference frame designed to match Newcomb's" print "# Tables of the Sun in Astronomical Papers Prepared for the Use of" pring "# the American Ephemeris and Nautical Almanac, Volume VI, 1895)"
as is nicely explained with full references https://en.wikipedia.org/wiki/Newcomb%27s_Tables_of_the_Sun -- Steve Allen <sla@ucolick.org> WGS-84 (GPS) UCO/Lick Observatory--ISB 260 Natural Sciences II, Room 165 Lat +36.99855 1156 High Street Voice: +1 831 459 3046 Lng -122.06015 Santa Cruz, CA 95064 https://www.ucolick.org/~sla/ Hgt +250 m
Steve Allen wrote:
In addition to the listed changes I suggest being more specific about the meaning of UT1 in leapseconds.awk by defining what is meant by "space".
Space is a fairly large topic and I'm not sure we need to go that far. leapseconds.awk's readers typically don't need to know things like Newcomb's Tables of the Sun and it'll save us work to just cite good leap second sources and get out of the way. For example, ICRF (used to define UT1) changed in January, and we dodged the hassle of updating leapseconds.awk by not mentioning ICRF there. In looking this over, though, I see that leapseconds.awk was a bit overenthusiastic about what UT1 is, and I attempted to make it more accurate via the attached patch.
On Thu 2019-07-04T12:59:45-0700 Paul Eggert hath writ:
- print "# (which measures the true angular orientation of the earth in space)" + print "# (a proxy for Earth's angle in space corrected for polar motion)"
That's a 1950s-lingo explanation from the era when it was not possible to measure the sub-diurnal variations of earth orientation so it was still possible to use simple models that were based on the existence of an axis of rotation relatively fixed to the surface of the earth. Current measurement precision requires general treatment of total body angular momentum and crustal angular velocity with a conventional model that does not match the 1950s notion of polar motion. The aim is for the current model to be continuous in value and rate with the reference frame of Newcomb, even though that was neither inertial nor a long-term measure of mean solar time. -- Steve Allen <sla@ucolick.org> WGS-84 (GPS) UCO/Lick Observatory--ISB 260 Natural Sciences II, Room 165 Lat +36.99855 1156 High Street Voice: +1 831 459 3046 Lng -122.06015 Santa Cruz, CA 95064 https://www.ucolick.org/~sla/ Hgt +250 m
Steve Allen wrote:
+ print "# (a proxy for Earth's angle in space corrected for polar motion)" That's a 1950s-lingo explanation
Thanks for the review. I cribbed that "polar motion" from Levine's 2016 article - I wonder what dusty old paper he got it from? Anyway, I installed the attached to try to improve the language. We needn't go into details like CIO, TIO, etc. since this file is about leap seconds not UT1.
On Thu 2019-07-04T15:34:31-0700 Paul Eggert hath writ:
Anyway, I installed the attached to try to improve the language. We needn't go into details like CIO, TIO, etc. since this file is about leap seconds not UT1.
That language deftly removes the objections. -- Steve Allen <sla@ucolick.org> WGS-84 (GPS) UCO/Lick Observatory--ISB 260 Natural Sciences II, Room 165 Lat +36.99855 1156 High Street Voice: +1 831 459 3046 Lng -122.06015 Santa Cruz, CA 95064 https://www.ucolick.org/~sla/ Hgt +250 m
On 2019-07-04 16:29, Steve Allen wrote:
On Thu 2019-07-04T00:35:32-0700 Paul Eggert hath writ:
Subject: [tz] [PROPOSED] Cite Rec. ITU-R TF.460-6 for leap seconds In addition to the listed changes I suggest being more specific about the meaning of UT1 in leapseconds.awk by defining what is meant by "space".
print "# The International Earth Rotation and Reference Systems Service" print "# periodically uses leap seconds to keep UTC to within 0.9 s of UT1" print "# (which measures the true angular orientation of the earth in space)"
to
print "# The International Earth Rotation and Reference Systems Service" print "# periodically uses leap seconds to keep UTC to within 0.9 s of UT1" print "# (which is a measure of the angular orientation of the earth's crust" print "# with respect to a reference frame designed to match Newcomb's" print "# Tables of the Sun in Astronomical Papers Prepared for the Use of" pring "# the American Ephemeris and Nautical Almanac, Volume VI, 1895)"
as is nicely explained with full references https://en.wikipedia.org/wiki/Newcomb%27s_Tables_of_the_Sun
Certainly the parameters in the modern definition of UT1 were chosen so that UT1 is continuous in phase and rate with Newcomb's definition of UT based on his tables of the Sun. But I find it a bit misleading to imply that only this match was the goal of the modern definition of UT1. The rotating body, the reference for measuring rotation angle, and the rotation axis have all been changed significantly since Newcomb's time around 1900. For one thing, the rotation described by modern UT1 is not that of the Earths's crust but that of the Earth-centered reference system ITRS; the Earth's crustal plates are moving with respect to the ITRS both secularly and with short periods (Earth tides). The exact coordinates of Greenwich in the ITRS change subdaily and secularly. Furthermore, the modern definition of UT1 is independent of the movement of the Sun, it only depends on the rotation of the reference system ITRS around an axis with respect to a celestial sphere defined by distant quasars taken as non-moving references (although that sphere is still affected by very small relativistic rotations that indeed do depend on the moving Earth). Finally, the axis of the rotation described by UT1 is not the instantaneous direction of the Earth's rotational angular momentum (in some reference system) but of a mean over 2 days (2 rotations). This is a practical measure to ensure that UT1 does not depend on short period movements of the terrestrial pole that are not induced by location-independent effects. Michael Deckers.
On Thu 2019-07-04T21:18:42+0000 Michael H Deckers hath writ:
Certainly the parameters in the modern definition of UT1 were chosen so that UT1 is continuous in phase and rate with Newcomb's definition of UT based on his tables of the Sun. But I find it a bit misleading to imply that only this match was the goal of the modern definition of UT1. The rotating body, the reference for measuring rotation angle, and the rotation axis have all been changed significantly since Newcomb's time around 1900.
In the change from FK3 to FK4 there was a step of 0.0016 s in UT2(BIH) at 1962-01-01, but that was inconsequentially small by comparison with the systematic offsets that had previously existed between time services of different nations up to that point https://www.ucolick.org/~sla/leapsecs/seasonal.html Bulletin Horaire series 5 number 16 indicates that as part of the change from FK3 to FK4 BIH had been instructed to recalculate the longitude of every observatory in a globally-consistent fashion so that the longstanding systematic offsets between their time values would be nulled. In section 3 Aoki et al. explicitly say that matching rate and value of UT1 was part of the agreement in the change from FK4 to FK5 https://ui.adsabs.harvard.edu/abs/1982A%26A...105..359A/abstract In section 7 Capitaine et al. note that in the change from FK5 to ICRS continuity of value was possible but that continuity of rate was only possible as a mean over an interval (instead of instantaneously) https://ui.adsabs.harvard.edu/abs/2003A%26A...406.1135C/abstract At each change the papers explaining the new system explicitly note the goal to preserve UT1 as continuous in rate and value with Newcomb's expressions in Tables of the Sun inasmuch as was possible while adopting a more precise set of conventions. Comments in tz do not need to review a century of changes of nomenclature and conventions, but they can legitimately say that much. -- Steve Allen <sla@ucolick.org> WGS-84 (GPS) UCO/Lick Observatory--ISB 260 Natural Sciences II, Room 165 Lat +36.99855 1156 High Street Voice: +1 831 459 3046 Lng -122.06015 Santa Cruz, CA 95064 https://www.ucolick.org/~sla/ Hgt +250 m
participants (3)
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Michael H Deckers -
Paul Eggert -
Steve Allen