lunartime.org

Primary documents on lunar time

Five documents decide what lunar time is today. Each one is read here in full: what it settles, what it leaves open, and which passages matter.

Key facts

  • Five documents carry the whole subject: one policy memorandum, two IAU resolutions, one peer-reviewed paper and one draft resolution. [1]Official
  • The oldest of the five is the OSTP memorandum of 2 April 2024, which names Coordinated Lunar Time (LTC). [2]Official
  • IAU Resolution II of 2024 defines the Lunar Celestial Reference System and its coordinate time, TCL. [3]Official
  • The 56.02 µs per day figure for a selenoid clock against a geoid clock comes from the NIST framework of 12 August 2024. [4]
  • Only one of the five is still open: Draft Resolution D is item 17 on the provisional agenda of the 28th CGPM. [1]Official

Almost everything written about lunar time comes from five documents. Two of them are resolutions, one is a national policy memorandum, one is a peer-reviewed paper, and one has not been voted on yet. They were written by different bodies for different purposes, and they do not say the same thing.

Each page below reads one document: the metadata card, a plain-language summary, what it decides, what it leaves open, and the passages worth quoting word for word. Quotations come from our register of verbatim passages, never from memory.

The five documents

The five primary documents, oldest first, with the status of each.
DocumentIssuerDateTypeStatusLink
OSTP Celestial Time Standardization memo (2024)White House Office of Science and Technology PolicyPolicy memorandumIn forceOriginal [2]Official
IAU 2024 Resolution II: LCRS and TCLInternational Astronomical Union, Commission A3ResolutionAdoptedOriginal [3]Official
IAU 2024 Resolution III: a coordinated lunar timeInternational Astronomical Union, Commission A3ResolutionAdoptedOriginal [5]Official
NIST's relativistic framework for lunar clocksNational Institute of Standards and Technology / The Astronomical JournalPeer-reviewed paperProposedOriginal [4]
CGPM 2026 Draft Resolution D on lunar timeBureau International des Poids et Mesures / CIPMDraft resolutionDraftOriginal [1]Official

How they fit together

Read in order, the five documents answer four different questions. The first gives the standard a name and a deadline. The second and third define the physics and ask for an agreement. The fourth supplies the numbers. The fifth is where an international decision could be taken.

Where each of these tracks stands today, and which milestone is next, is kept on the standards tracker. The same events in date order are on the timeline.

What none of them does

None of the five realizes a lunar time scale. There is no ensemble of clocks on the Moon, no published offset and no bulletin[5]Official. Values shown elsewhere on this site are model values computed from these definitions[6].

If you are starting from zero, read what Coordinated Lunar Time is first, then come back to the documents. The glossary defines the abbreviations these documents use.

The peer-reviewed papers and preprints that put numbers on these definitions are read one at a time in the papers hub.

How we choose these documents, check that every URL still opens, and correct a page when it turns out to be wrong is set out in about lunartime.org.

Sources

  1. Convocation of the 28th meeting of the CGPM (O/Ref AK-CFA-2026-1001) — Bureau International des Poids et Mesures / CIPM, . Official document. Verified .
  2. Policy on Celestial Time Standardization — White House Office of Science and Technology Policy, . Official document. Verified .
  3. Resolution to establish a standard Lunar Celestial Reference System (LCRS) and Lunar Coordinate Time (TCL) — International Astronomical Union, Commission A3 — XXXII General Assembly, . Official document. Verified .
  4. A Relativistic Framework to Estimate Clock Rates on the Moon — Neil Ashby and Bijunath R. Patla, NIST — The Astronomical Journal 168:112, . Peer-reviewed. Verified .
  5. Resolution on the establishment of a coordinated lunar time standard by international agreement — International Astronomical Union, Commission A3 — XXXII General Assembly, . Official document. Verified .
  6. Our calculation: the lunartime.org clock model — Lunartime Editorial, . Our calculation. Verified .

Last verified