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The coming decade will see a resurgence in lunar exploration — including dozens of missions and plans to establish permanent bases on the Moon. The endeavours pose myriad challenges. Among them is a subtle, but fundamental, question that metrologists worldwide are working to answer: what time is it on the Moon?
“We’re just starting to lay this out,” says Cheryl Gramling, an aerospace engineer who leads the position, navigation and timing team at NASA’s Goddard Space Flight Center in Greenbelt, Maryland.
The Moon doesn’t currently have an independent time. Each lunar mission uses its own timescale that is linked, through its handlers on Earth, to coordinated universal time, or ut c — the standard against which the planet’s clocks are set. But this method is relatively imprecise and spacecraft exploring the Moon don’t synchronize the time with each other. The approach works when the Moon hosts a handful of independent missions, but it will be a problem when there are multiple craft working together. Space agencies will also want to track them using satellite navigation, which relies on precise timing signals.
It’s not obvious what form a universal lunar time would take. Clocks on Earth and the Moon naturally tick at different speeds, because of the differing gravitational fields of the two bodies. Official lunar time could be based on a clock system designed to synchronize with utc , or it could be independent of Earth time.