International Metrology Body Sets Up Framework for a Standard Lunar Time Scale

At the 28th General Conference on Weights and Measures in Versailles, member states approved a resolution to establish an international reference scale for lunar time, a step deemed essential for upcoming Moon exploration programs. Earth’s Coordinated Universal Time (UTC) is unsuitable on the Moon because general-relativity predicts a faster passage of time there, creating a 56-microsecond per day discrepancy between Earth-based and lunar clocks.

While seemingly minor, this offset can cause navigation errors of about a meter, which mission designers cannot tolerate. Pascale Defraigne of the Royal Observatory of Belgium and NASA project coordinator Joel Parker emphasized that achieving meter-scale positioning on the lunar surface requires timing precision on the order of a nanosecond. The new framework aims to harmonize time-keeping standards across space agencies from the United States, China, India, Japan, Europe and others that intend to deploy lunar navigation satellites. Questions remain about how to build a lunar clock network, what altitude reference will replace sea level, and which organization will oversee the system, but the resolution marks a coordinated effort to align lunar and terrestrial timekeeping.