On Dec. 8, 2025, the Purple Mountain Observatory in Nanjing, China published a paper in Astronomy and Astrophysics about the Lunar Time Ephemeris, or simply the LTE400, a software which is helping to solve a major issue in astronomy: the time difference between Earth and the Moon. Compared to Earth, the Moon ticks approximately 56 millionths of a second faster per day on the current clock system due to the difference in gravity. While never proving to be an issue before, a difference of a microsecond could quickly become significant in future navigation systems. The LTE400 is able to account for both the Moon’s weaker gravity and its motion through space, allowing events on the Moon to be accurately synchronised with clocks used on Earth.
It started in 2024, when the International Astronomical Union pushed for the broad framework of the Moon to have its own time reference. To build that system, the Purple Mountain Observatory began with the data of the Moon’s motion to begin tracking how the time difference between the Earth and the Moon changes over time. The LTE400 takes the created calculations and automates the process, allowing anyone to compare lunar and Earth time. While its creation is a huge step forward in space time keeping, it’s still in its early stages and many advancements are still being made to allow for real time support in navigation and lunar clock networks.
Besides being used for space travel, the LTE400 is also a huge step in the future of lunar colonies. By being able to compute the complex formulas at the rate the program does, eventually some of the first lunar settlers will be able to live comfortably knowing that their clocks are perfectly in sync. Also, the Purple Mountain Observatory has made the LTE400 software available on Github at no cost.
To view the original paper, head to: https://www.aanda.org/articles/aa/full_html/2025/12/aa57345-25/aa57345-25.html
And to view the publicly available github release, head to: https://github.com/xlucn/LTE440?tab=readme-ov-file
