What happens after the votes at the 28th CGPM
Key facts
- The conference has not met. Draft Resolutions C and D can each be carried, amended on the floor, or left aside. [1]Official
- A United States memorandum of 2 April 2024 asks NASA for a finalized lunar timing implementation strategy no later than 31 December 2026. [2]Official
- That deadline is national policy and does not depend on the outcome at the 28th CGPM. [2]Official
- Lunar Coordinate Time (TCL) is already defined by IAU Resolution II of 2024 and stays defined either way. [3]Official
- If Draft Resolution C is left aside, the 2022 deadline stands on its own: the limit on UT1 minus UTC is still to be increased in, or before, 2035. [4]Official
The title of this page assumes nothing. The 28th CGPM is scheduled for October 2026, and the outcome of a diplomatic conference is not predictable from its agenda [1]Official. Two time drafts are in play. Draft Resolution C, on the continuity of UTC, is item 16; Draft Resolution D, on a lunar reference time scale, is item 17 [1]Official. Each can be carried, amended on the floor, or left aside, and the two votes are independent of each other.
So this page covers both outcomes for both drafts. It also lists what would not change in any of them, which is the longer list.
The two outcomes for the lunar draft
If the conference carries the draft, the definition of an international lunar reference time scale, and its traceability to UTC, becomes a resolution of the CGPM. That is the subject of the text sent to member states [1]Official.
If it does not, the latest word on the subject stays where it is now: a coordinate time defined by the IAU in 2024 [3]Official, a request from the IAU that international organizations agree the relations between the scales [5]Official, and technical work in the CCTF with space agencies [6]Official.
Neither outcome produces a clock reading. That distinction is the subject of what is Coordinated Lunar Time.
The two outcomes for the leap second draft
If the conference carries Draft Resolution C, 20 May 2027 stops being a proposal and becomes the implementation date named in a resolution of the CGPM. That date comes from Decision CIPM/115-5 of 2026, which endorsed the updated draft for presentation at this meeting [7]Official.
If it does not, the earlier decision stands on its own. Resolution 4 of the 27th CGPM, in 2022, already decides that the maximum value for the difference UT1 − UTC will be increased in, or before, 2035 [4]Official. A rejected draft would remove the proposed date, not the 2035 deadline.
Neither outcome changes the practice this year. No leap second has been announced for the end of June 2026 or the end of December 2026, and TAI − UTC has stayed at 37 seconds since 1 January 2017 [8]Official. Neither outcome states a size for the new limit either, because no published decision states one [4]Official. The chain of documents behind the proposed date is set out in leap seconds and the October vote.
What changes and what does not
| Draft | Question | If the draft is carried | If it is not | Source |
|---|---|---|---|---|
| C | Is 20 May 2027 an implementation date in a CGPM resolution? | Yes, as fixed in the updated draft endorsed by Decision CIPM/115-5 | No; only the 2022 deadline of 2035 stands | [7]Official |
| C | Is the limit on UT1 − UTC still due to be increased? | Yes, in, or before, 2035 | Yes, in, or before, 2035 | [4]Official |
| C | Is a size for the new limit published? | No; no decision states one | No | [4]Official |
| C | Does TAI − UTC change on the day of the vote? | No; it stays 37 seconds | No | [8]Official |
| D | Is a lunar reference scale defined internationally? | Yes, by a resolution of the CGPM | No; the IAU coordinate time of 2024 remains the latest step | [1]Official |
| D Is a scale being computed? | No; a definition is not a realization | No | [6]Official | |
| D Is TCL still defined? | Yes, by IAU Resolution II of 2024 | Yes | [3]Official | |
| D Who computes the scale? | Not named in the draft | Not named anywhere | [1]Official | |
| Both | Does the US deadline of 31 December 2026 move? | No; it is set by national policy | No | [2]Official |
The deadlines that hold either way
The United States set its own dates before the conference was convened. The memorandum of 2 April 2024 asks NASA, with the Departments of Commerce, Defense, State and Transportation, for a finalized strategy to implement lunar timing standardization no later than 31 December 2026 [2]Official. The same memorandum set two earlier dates, both 31 December 2024: consideration of Coordinated Lunar Time in the annual Moon-to-Mars Architecture Concept Review, and a milestone-based approach delivered to OSTP [2]Official.
NASA announced the work publicly in September 2024 [9]Official. None of those dates is conditional on a vote in Versailles, and none of them is moved by one [2]Official.
The standards tracker carries the same dates track by track, and the timeline puts them in order with everything that came before.
What we would change on this site
If a draft is carried, the BIPM row on the standards tracker moves to the next stage, and every page that calls that text a proposal is rewritten the same day. If it is not, the row stays where it is and the page says so. The stages are defined on the tracker itself, and a row moves only when a document says it moved.
Either way, no clock value on this site changes. Our figures come from the published relativistic model, not from a resolution, and a vote does not alter physics [10].
Read next
The lunar text is covered in what Draft Resolution D proposes; the leap second text in leap seconds and the October vote; the procedure that decides it is in how the CGPM votes on a draft resolution; the other two time drafts are in three time resolutions at the 2026 CGPM [1]Official.
The primary text sits on the document page for Draft Resolution D, and the rest of our coverage is in the lunar time news hub.
The agenda itself, item by item, and the place where each result will be published, are kept on our hub for the 28th CGPM.
Sources
- Convocation of the 28th meeting of the CGPM (O/Ref AK-CFA-2026-1001)
- Policy on Celestial Time Standardization
- Resolution to establish a standard Lunar Celestial Reference System (LCRS) and Lunar Coordinate Time (TCL)
- Resolution 4 of the 27th CGPM (2022): On the use and future development of UTC
- Resolution on the establishment of a coordinated lunar time standard by international agreement
- Latest Updates from 2025 CCTF Meeting
- Meetings of the CIPM: Outcomes
- Value of TAI-UTC (IERS leap second data file)
- NASA to Develop Lunar Time Standard for Exploration Initiatives
- Our calculation: the lunartime.org clock model
Last verified