On 2026-08-22 16:09, Arthur Olson via tz wrote:
"Greenwich moon time? The high-stakes race to set lunar clocks."
Thanks for the heads-up, as the Theory file was getting stale on the subject of
lunar timekeeping standardization. I installed the attached to try to keep up,
though it'll likely need further changes after October.
From 00390a07d0d8c8a5c6519849d149245cc7d1f714 Mon Sep 17 00:00:00 2001
From: Paul Eggert <[email protected]>
Date: Sat, 22 Aug 2026 18:03:04 -0700
Subject: [PROPOSED] Lunar time coordination updates
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Heads-up from ADO in:
https://lists.iana.org/hyperkitty/list/[email protected]/thread/WCUGUFDIP7QSAJBAV7CYQLC4G3THDKUI/
* theory.html: For lunar time, mention China’s TCL and the BIPM.
---
theory.html | 24 +++++++++++++++++-------
1 file changed, 17 insertions(+), 7 deletions(-)
diff --git a/theory.html b/theory.html
index bbc9d693..91fb6bbb 100644
--- a/theory.html
+++ b/theory.html
@@ -1450,17 +1450,27 @@ They sometimes disagree.
<section>
<h2 id="planets">Time and time zones off Earth</h2>
<p>
-The European Space Agency is <a
-href="https://www.esa.int/Applications/Satellite_navigation/Telling_time_on_the_Moon";>considering</a>
-the establishment of a reference timescale for the Moon, which has
+Efforts are underway to establish a reference timescale for the Moon, which has
days roughly equivalent to 29.5 Earth days, and where relativistic
effects cause clocks to tick slightly faster than on Earth.
-Also, <abbr title="National Aeronautics and Space Administration">NASA</abbr>
-has been <a
+The European Space Agency <a
+href="https://www.esa.int/Applications/Satellite_navigation/Telling_time_on_the_Moon";>began
+considering</a> the problem in 2023, and in 2024
+<abbr title="National Aeronautics and Space Administration">NASA</abbr>
+was <a
href="https://bidenwhitehouse.archives.gov/wp-content/uploads/2024/04/Celestial-Time-Standardization-Policy.pdf";>ordered</a>
to consider the establishment of Coordinated Lunar Time (<abbr>LTC</abbr>).
-It is not yet known whether the US and European efforts will result in
-multiple timescales on the Moon.
+In 2025 a team at China’s
+<a href="https://en.wikipedia.org/wiki/Purple_Mountain_Observatory";>Purple
+Mountain Observatory</a> published
+<a href="https://doi.org/10.1051/0004-6361/202557345";>Lunar Time Ephemeris
+440</a>, the first formal proposal for a standard
+for Temps Coordonné Lunaire (<abbr>TCL</abbr>).
+A <a href="https://www.bipm.org/documents/20126/284836054/CGPM-2026-Draft-Resolutions.pdf";>draft
+resolution of the 13–15 October 2026 General Conference on Weights
+and Measures</a> recommends that the <a href="https://www.bipm.org/en/";>Bureau
+International des Poids et Mesures</a> collaborate with space agencies
+and other organizations on this matter.
</p>
<p>
--
2.53.0
