China and lunar time: what has been published
Key facts
- Xu Lu, Tian-Ning Yang and Yi Xie of the Purple Mountain Observatory, Chinese Academy of Sciences, published the lunar time ephemeris LTE440. [1]
- LTE440 computes Lunar Coordinate Time and its relations with TCB and TDB, with accuracy better than 0.15 ns before 2050. [1]
- The user manual states that the package follows the definition of Lunar Coordinate Time given in IAU 2024 Resolution II. [2]
- Reporting of 25 June 2026 described the United States and China as working towards different lunar time arrangements. [3]
- Every lunar clock value on this site is a model value, because no lunar time scale has been realized anywhere. [4]
A search for a Chinese lunar time standard usually lands on one group of papers. This page sets out what those papers state, and names the source for each statement.
What has been published is software and a definition. It is not an operating clock service, and none of the papers claims that it is.
Who published what
Xu Lu, Tian-Ning Yang and Yi Xie of the Purple Mountain Observatory, Chinese Academy of Sciences, published a lunar time ephemeris called LTE440 [1]. The journal version appeared in Astronomy & Astrophysics 704, A76, dated 23 September 2025 [1].
The same three authors posted a user manual for the same package on 24 June 2025 [2]. The two documents describe one system and agree wherever both quote a number.
What LTE440 computes
LTE440 calculates Lunar Coordinate Time and its relations with Barycentric Coordinate Time and Barycentric Dynamical Time [1]. The manual states that the package follows the definition of Lunar Coordinate Time given by the International Astronomical Union in its 2024 Resolution II [2].
That resolution is the same document that fixes the epoch of the lunar coordinate time [5]Official. The Chinese work therefore builds on the international definition rather than on a separate one.
The authors integrate the relativistic time-dilation integral on the JPL DE440 ephemeris and export the result in the SPICE format [1]. Mission software that already reads SPICE can read the transformation directly.
The documents this page rests on
Our registry holds four sources for this subject. Three are peer-reviewed papers; one is a press report. The table lists each one and what it states.
| Document | Date | Type | What it states | Source |
|---|---|---|---|---|
| LTE440: definitions, algorithm and performance | 23 September 2025 | Peer-reviewed | accuracy better than 0.15 ns before 2050, numerical precision about 1 ps over the full span | [1] |
| LTE440: User Manual | 24 June 2025 | Peer-reviewed | the package follows the TCL definition of IAU 2024 Resolution II; annual term about 1651 µs, monthly term 126 µs | [2] |
| Two birds with one stone | 28 December 2025 | Peer-reviewed | a single orbital clock could realize both a lunar coordinate time and a lunar geoid time | [6] |
| What time is it on the moon? The US and China disagree | 25 June 2026 | Press | the United States and China are working towards different lunar time arrangements | [3] |
The secular drift between the coordinate times is stated as 1 − 1.4825362167 × 10⁻⁸ for TCL against TCB, and as 1 + 6.79835524 × 10⁻¹⁰ for TCL against TDB [1]. Both compare two coordinate times, so neither is the Moon-against-Earth rate quoted elsewhere on this site.
A second paper from the same line
Tian-Ning Yang and Yi Xie also appear as authors of a proposal for a single orbital clock that would realize two lunar time options at once [6]. We read that paper in two birds with one stone, and LTE440 itself in the LTE440 read.
Read together, the two works show one group publishing both the conversion arithmetic and a way to realize a reference clock [6].
Where reporting says the two countries differ
Our only source for a disagreement is journalism, not a document. Space.com reported on 25 June 2026 that the United States and China are working towards different lunar time arrangements [3].
We give that report less weight than the papers above, and say so plainly. The papers are peer-reviewed and state what they compute; the report is press and describes how two programmes are positioned [3].
Our registry holds no official Chinese government document on lunar time. Until it does, this page describes published research and nothing more.
What is not settled
- No realized scale. LTE440 converts between definitions, not between running clocks, and every lunar clock value we print is a model value [4].
- No named operator. None of these papers says which body would run a lunar time service, or when.
- No agreed tie to UTC. IAU Resolution III asks international organizations to agree the relations between a lunar reference time scale, a lunar coordinate time and UTC [7]Official.
Where each organization stands, with dates, is on the standards tracker. What the proposed standard is called and who named it is in what Coordinated Lunar Time is, and the practical side of converting a timestamp today is in lunar time for developers. The Learn hub lists the rest.
Sources
- Lunar Time Ephemeris LTE440: definitions, algorithm and performance
- Lunar Time Ephemeris LTE440: User Manual
- What time is it on the moon? The US and China disagree
- Our calculation: the lunartime.org clock model
- Resolution to establish a standard Lunar Celestial Reference System (LCRS) and Lunar Coordinate Time (TCL)
- Two birds with one stone: simultaneous realization of both Lunar Coordinate Time and lunar geoid time by a single orbital clock
- Resolution on the establishment of a coordinated lunar time standard by international agreement
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