CGPM 2026 Draft Resolution D on lunar time

In plain language

The General Conference on Weights and Measures is the diplomatic body of the Metre Convention. Its 28th meeting is scheduled for 13–15 October 2026 at the Palais des Congrès de Versailles ^[2]Official.

Lunar time is on that agenda. The convocation circulated to member states on 13 January 2026 lists it as item 17 of the provisional agenda and as Draft Resolution D ^[1]Official. A draft resolution is a proposal: delegates may adopt it, amend it or leave it aside.

This is the only document of the five that has decided nothing. It is listed here because it is the nearest scheduled decision point on the subject, and because the wording that reaches the floor is already public ^[1]Official.

What it decides

• Nothing yet. The conference has not met, no vote has been taken, and the text can still change before it is put to member states ^[1]Official.
• The title is fixed. The subject of the draft is quoted verbatim below, from the convocation itself ^[1]Official.
• Its place on the agenda is fixed. Lunar time is item 17 of the provisional agenda and carries the letter D among six drafts ^[1]Official.
• Two CIPM decisions are on the record. Decision CIPM/115-6 approved forwarding an updated draft to the conference, and decision CIPM/115-14 refined its wording ^[3]Official.
• The preparatory work is public. The CCTF has been working with space agencies on a lunar reference time scale and has held workshops with lunar system providers ahead of the conference ^[4]Official.

What it leaves open

• Whether it is adopted. The outcome of a diplomatic conference is not predictable from its agenda, and we make no forecast ^[1]Official.
• In which wording. Draft texts are routinely amended before a vote ^[3]Official.
• Who would hold the scale. No organization has been designated as the keeper of a lunar reference time scale ^[5]Official.
• What traceability to UTC would mean in practice. A definition of traceability has to name a comparison method and an uncertainty budget, and neither is on the public record yet ^[6].

Key passages

The subject of the draft, as the convocation states it ^[1]Official.

On the definition of an international lunar reference time scale and its traceability to UTC

The CIPM has already recorded one substantive position on the question. Decision CIPM/115-14 refined the draft so that it asks for one scale, while allowing more than one realization of it ^[3]Official.

there must be a unique lunar reference time scale, even if there may be several realizations

That distinction matters for the glossary entry on weighted clock ensembles: a single scale computed from several independent realizations is how terrestrial time already works, and the entry for UTC describes the same arrangement on Earth ^[4]Official.

The six draft resolutions of the 28th CGPM

The convocation lists six draft resolutions, lettered A to F. Only D concerns lunar time; the other five are the metrological business of the same conference. The titles below are quoted from the convocation ^[1]Official.

Letter	Title, verbatim from the convocation	Source
A	On universal adherence to the Metre Convention	[1]Official
B	On the future definition of the second	[1]Official
C	On the technical actions needed to ensure the continuity of UTC	[1]Official
D	On the definition of an international lunar reference time scale and its traceability to UTC	[1]Official
E	On the further digital transformation of the global metrology system	[1]Official
F	On the adoption of Rules of Procedure of the General Conference on Weights and Measures	[1]Official

The letters differ between two BIPM sources. The CIPM outcomes page uses an earlier, intermediate lettering from the committee stage, in which the digital transformation draft is B and the redefinition of the second is E ^[3]Official. The convocation of 13 January 2026 is the document sent to member states, so this site follows its lettering and treats the CIPM page as the earlier stage of the same work ^[1]Official.

Where this sits among the other steps: IAU Resolution III asked international organizations to agree the relations between the scales, and the OSTP memorandum set a national deadline of 31 December 2026 ^[7]Official. The standards tracker records the conference as the next dated milestone, the timeline lists it as a scheduled event, and will the Moon have time zones covers what a lunar scale would mean for people working on the surface.

Our coverage of this draft

Four articles work through the same conference from different angles, and all four were written before it met ^[1]Official.

• Three time resolutions at the 2026 CGPM — why three of the six drafts are about time ^[1]Official.
• What CGPM Draft Resolution D proposes — the subject of this text, and the questions it leaves open.
• How the CGPM votes on a draft resolution — who is entitled to vote, and at which agenda item.
• What happens after the vote on lunar time — both outcomes, and the dates that hold either way.

The hub for all of it is lunar time news.