Coordinated Lunar Time (CLT) is a request from the Joe Biden administration to NASA due to the difference in gravitational field strength on the Moon, which makes time pass faster relative to Earth. That's just 58.7 microseconds per day, which may not sound like a lot, but when it comes to spacecraft synchronization, it can make a big impact.

“The basic theory of gravity in our universe leads to the fact that time passes differently in different places in the universe. Gravity on the Moon is a little weaker and clocks work differently.” BBC Catherine Heymans, Director of the Royal Observatory in Edinburgh, Scotland.

Time on Earth is measured by hundreds of atomic clocks placed around the planet, which measure the changing energy states of atoms to record time to the nanosecond. If they were put on the moon, they would run one second faster in 50 years.

“The atomic clock on the Moon will have a different rhythm than the clock on Earth,” explains Kevin Coggins, NASA's communications and navigation officer. “It makes sense that when you go to another body, like the Moon or Mars, they each have their own heart rate,” he added.

But NASA isn't the only one trying to determine lunar time. The European Space Agency (ESA) is also developing a new lunar time system, a topic that will require agreement between countries and a central coordinating body – currently this task falls to the International Space Agency.International Bureau of Weights and Measures), an intergovernmental body with 64 member states (including Portugal), headquartered in the suburbs of Paris.

Currently, Coordinated Universal Time (UTC) is used on the International Space Station, since it is in low orbit. UTC is the reference time zone by which all other time zones in the world are calculated and corresponds to winter time in mainland Portugal (i.e. UTC is currently one hour lower than in mainland Portugal).

The United States wants Coordinated Lunar Time to become a reality in 2026, in time for its manned mission to the Moon. Artemis-3 will be the first North American mission to return to the lunar surface since Apollo 17 in 1972.