US and China disagree on what time it is on the Moon and that could become a serious problem for future lunar missions

"What time is it?" is one of the oldest and most universal questions humans ask. On Earth, the answer changes every second, but everyone agrees on how to measure it. That consensus may not exist on the Moon between two of the world's space powers, the United States and China.

The disagreement may sound trivial at first. After all, how much difference can a few millionths of a second make? According to scientists, the answer is enough to jeopardize spacecraft navigation, satellite coordination, autonomous landings, and even future lunar bases.

As both countries accelerate plans to establish a long-term human presence on the Moon, they are also racing to build separate navigation and communication networks. Those systems depend on extremely precise timekeeping, making lunar time one of the next major strategic battlegrounds in space.

Why time on the Moon is different from time on Earth

Unlike clocks on Earth, clocks on the Moon do not tick at exactly the same rate. Because the Moon experiences weaker gravity than Earth, precisely 1/6, a consequence explained by Albert Einstein's theory of relativity, time actually passes slightly faster there.

Scientists now estimate that a clock on the Moon gains roughly 56 microseconds every day compared with one on Earth. That may seem insignificant, but navigation systems cannot tolerate even such tiny differences.

As National Institute of Standards and Technology (NIST) physicist Bijunath "Biju" Patla explained to Science.org in 2024, "Earth is way bigger than the Moon, and gravity slows down time. Since the Moon is away from Earth, it has slightly less gravitational pull. And so time there is going to tick faster than on Earth."

Those tiny differences accumulate continuously, eventually becoming large enough to affect spacecraft positioning.

Why a few microseconds can mean hundreds of metres

Modern navigation systems, including GPS, depend almost entirely on precise timing. GPS satellites constantly broadcast synchronized timestamps. Your phone calculates its position by measuring how long those signals take to arrive.

If satellite clocks disagree by even a single microsecond, location estimates can shift by hundreds of meters. The same principle applies to future Moon missions. Patla explained, "If you send communications, observers on the Moon and on Earth are off by a few microseconds. And it keeps adding over time and becomes a huge time difference."

He added, "If we are to land a spacecraft on the Moon precisely, within meters, then we need to know the common time between Earth and the Moon."

Scientists have refined lunar timing calculations over the years. "Before, there were different calculations of lunar time, ranging from 56 to 58 microseconds faster per day. Now, we know that it is 56.02 microseconds per day. If we were to navigate with this accuracy, we would be within 10 meters of error," he further explained.

NASA wants a universal lunar clock

Recognizing the challenge, the White House directed NASA to develop Coordinated Lunar Time (LTC), a standardized time reference that would serve future Moon operations. NASA envisions LTC becoming the backbone of LunaNet, an internet-like communications and navigation network for lunar exploration.

Instead of every spacecraft relying independently on Earth-based clocks, missions would synchronize through a shared lunar time standard.

Scientists even plan to place dedicated atomic clocks on the Moon. Patla explained to the outlet that “people have plans to put clocks on the Moon," and a reference clock would likely be placed near the Moon's equator.

China is building a different lunar infrastructure

China, the only country to have successfully landed spacecraft on the Moon's far side, however, is developing its own lunar architecture. Its Chang'e lunar exploration program already operates the Queqiao-1 and Queqiao-2 relay satellites, the world's only active lunar communication relay satellites.

Unlike NASA, however, China has not committed to using Coordinated Lunar Time. That means future Chinese lunar satellites could operate on a different timing standard from NASA's LunaNet.

If two navigation systems cannot synchronize their clocks, spacecraft from different countries may struggle to communicate or coordinate safely.

Why this matters beyond science

The issue is not merely academic. Both the United States and China plan to send astronauts back to the Moon before the end of this decade.

NASA's Artemis program aims to establish a sustained human presence around the lunar south pole within a couple of years, while China hopes to land astronauts by 2030 and build an International Lunar Research Station by 2035.

Future lunar operations could involve autonomous spacecraft, robotic mining, cargo deliveries, satellite constellations, navigation services, and permanent research stations, and without compatible timing systems, these activities could become far more complicated and potentially dangerous.

Could the Moon have time zones?

Probably not. Asked whether the Moon might eventually have time zones or daylight saving time, Patla dismissed the idea. "For scientific applications, navigation, communication, you don't need a time zone or daylight savings."

He added, "In fact, time zones are hassle, it's an artificial thing for human convenience." Instead, scientists expect a single standardized lunar reference time that every spacecraft can use regardless of location.

The debate over lunar time is ultimately about far more than clocks. The nation whose timing standard becomes widely adopted could shape the navigation, communications, and operational framework that future lunar missions rely on, much as GPS transformed life on Earth.