China rolls out world’s first time system for moon
Nanjing scientists translate Einstein’s theory into practical engineering tools
BEIJING – Chinese scientists have released what they describe as the world’s first ready-to-use software designed specifically to keep time on the moon, a breakthrough aimed at supporting navigation, landings and future human activity beyond Earth.
Developed by researchers at the Purple Mountain Observatory in Nanjing, the system is intended to bridge the growing gap between Earth-based clocks and the way time flows on the lunar surface.
The move comes as lunar missions multiply and the moon shifts from being an occasional destination to a place where several spacecraft, and eventually people, are expected to operate at the same time. Precise timing is critical for spacecraft tracking, landing accuracy and the type of satellite navigation networks that planners hope to deploy around the moon.
Lunar timekeeping system
Clocks tick faster on the moon than on Earth because of its weaker gravity, a difference predicted by Albert Einstein’s theory of general relativity. The gap is about 56 millionths of a second per day. While tiny, the offset accumulates steadily, meaning that after months and years the mismatch becomes large enough to undermine navigation and positioning systems if it is not corrected.
Until now, engineers running lunar missions have relied on Earth time and applied bespoke corrections whenever needed. That approach worked when flights to the moon were rare and isolated. With multiple probes and landers now planned by different countries, those ad hoc fixes are increasingly impractical.
How it works
The Purple Mountain Observatory team built a detailed model that factors in both the moon’s weaker gravity and its motion through space, the South China Monitoring Post reports. By combining those effects, the software can translate between Earth time and lunar time with extreme precision. According to a paper published in the December issue of Astronomy and Astrophysics, the method remains accurate to within a few tens of nanoseconds even when projected over 1,000 years.
Those calculations have been packaged into a single tool called LTE440, short for Lunar Time Ephemeris. Instead of forcing engineers to run complex formulas, the software allows them to compare Earth and moon time in one step, making the system practical for everyday mission planning.
Experts say such tools are becoming essential rather than optional. Differences as small as a microsecond can quickly distort navigation calculations over short periods. If lunar equivalents of GPS are to be used for precision landings within the next few years, they say, a reliable way of handling time differences is required.
In 2024, the International Astronomical Union adopted a framework calling for the moon to have its own official time reference. LTE440 represents an early implementation of that idea, with the Chinese team noting it will need to be expanded to support real-time navigation and future lunar clock networks.