Timekeeping on the Moon

Timekeeping on the Moon is an issue of synchronized human activity on the Moon and contact with such. The two main differences to timekeeping on Earth is the length of a day on the Moon, being the lunar day or lunar month, observable from Earth as the lunar phases, and the differences between Earth and the Moon of how differently fast time progresses, with 24 hours on the Moon being 58.7 microseconds (0.0000587 seconds) faster, resulting from the different masses of the Moon and Earth, the effect being called gravitational time dilation.

As of early 2024, there is no lunar time standard. Instead, the time on the Moon is different for each country involved. Thus, American activities on the Moon run on the time zone of their mission control centre, while Chinese activities on the Moon run on China Standard Time. As more countries are active on the Moon and interact with each other, a different, unified system will be needed.

In 2024, the White House asked NASA to establish a unified Coordinated Lunar Time standard for the Moon and other celestial bodies by 2026.

The European Space Agency has proposed a lunar reference time for the Moon to solve this issue.

History


The technology used for the timekeeping devices deployed to the Moon have varied over the decades. Several Omega Speedmasters have been on the Moon, synched to Central Standard Time (CST).

The Apollo Guidance Computer (AGC) kept a triple-precision count of time in a real time clock cuing from a quartz oscillator; a standby option (although never used) would allow it to update this count every 1.28 second (~0.78 hertz) — more often when not standing by. In addition to maintaining the clock cycle, computer timekeeping allowed the AGC to display the capsule's vertical and horizontal movements relative to the Moon's surface, in units of feet per second.