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What time is it on the moon? Maybe we’ll know soon

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An artist's view of astronauts at work on the moon.

An artist’s view of astronauts at work on the moon. Credit: NASA.

By the end of this decade, the moon will be buzzing with activity. Our closest celestial neighbor will witness the arrival of the first crop of astronauts since the Apollo era, more than half a century ago. Dozens of robotic explorers will be stationed on and around it by multiple nations vying for permanent bases on the dark, pockmarked surface. As a revival of the lunar race draws closer, scientists have just begun to work out an important question: What time is it on the moon?

It turns out that the simple question has a complicated answer. Until now, lunar missions have operated on the time of their respective homelands. However, early last year the European Space Agency (ESA) deemed this system untenable for the coming wave of lunar missions.

Without a standard time for the moon, “there is a risk that something could go terribly wrong,” says Catherine Heymans, an astrophysicist at the University of Edinburgh in Britain. “This clock needs to be defined.” Multiple spacecraft from different countries are expected to be on or around the moon at the same time, underscoring the need for a common lunar time – and by extension, a navigation system – that would facilitate real-time communications, avoid collisions and conduct joint operations . operations, according to the ESA.

On April 2, more than a year after ESA identified the problem, the White House ordered NASA to implement new standardized lunar time by the end of 2026. This coordinated lunar time (LTC) is a necessity for the “safety and accuracy” of future lunar missions, Steve Welby, deputy director for national security at the White House Office of Science and Technology Policy, said in a statement on April 2.

“The White House intervention is very helpful because it really puts the foot on the accelerator to make this happen before the planned Artemis landing by the end of 2026,” Heymans said.

In addition, consistent lunar time is needed to create the moon’s own GPS, Welby said. Currently, scientists rely on a network of radio antennas to routinely ping spacecraft and calculate the time it takes for the spacecraft to ping back, from which scientists determine their locations. However, the Global Navigation Satellite System (GNSS), a small constellation of satellites that space agencies hope to make a reality by 2030, could provide better positioning in the same way GPS provides timing and location data to smartphones and maps in cars here on Earth. .

Timekeeping on the moon

For us earthlings, time does not change. Even if you are very bored and feel like time is passing painfully slowly, the seconds tick by at the same pace as always – each second is defined as 9,192,631,770 energy transitions within a cesium atom, which is the decades-long, ultra-precise method is of universal timekeeping.

Time passes just a little faster on the moon, where gravity is one-sixth that of Earth. For example, if you flew a clock from Earth – and waited fifty years for the offset to build up – the moon’s clock would run one second faster than the one on Earth.

“It feels like science fiction, but it’s not,” says Heymans. “This is a very solid prediction of general relativity, one of the best-tested theories we have that explains the structure of our universe.”

Related: How long is a year on other planets? | How much you would weigh on other planets

According to the theory of relativity, which Albert Einstein proposed over a century ago, atomic clocks located in different gravitational fields would tick at different speeds. This includes astronauts aboard the International Space Station, but their orbit is close enough to Earth that they can calibrate their clocks to Earth’s Universal Coordinated Time (UTC). However, human and robotic explorers who spend long periods on the moon would very slowly distance themselves from time on Earth. “It’s a very, very subtle difference,” says Heymans. “Time is not absolute.”

That minuscule difference wouldn’t be a problem if there was only one crew working on the moon, in which case these changes could be easily explained, she added. However, given the great interest from several countries, ‘accurate timekeeping becomes even more important’.

NASA’s proposed LTC time zone is “a system that, while independent, maintains traceability to Earth’s Coordinated Universal Time (UTC) to allow for seamless time conversion,” says Julian Coltre, public affairs officer at NASA’s Space Operations Mission Directorate.

Lunar timekeepers

It is unclear how space agencies will determine the time on the moon, and many technical details remain to be worked out. One of the open questions is whether lunar time should be maintained by placing atomic clocks on the moon or synchronized with Earth. In that case, a relay system would have to continuously communicate with our planet to record the time and transmit it to the moon’s inhabitants.

“This will take some study and planning, and this is how the agency will begin the process,” Coltre said. To learn more about how LTC compares to UTC: “NASA could try to conduct a demonstration mission with clocks on the moon’s surface, based on atomic clocks flying on spacecraft today.”

The craziest of all ideas is timing flashes of light from distant spinning stars known as pulsars. These are massively magnetized neutron stars that form from the collapsed remains of dead stars. As they spin, electromagnetic radiation emanating from their magnetic poles flashes toward Earth like a lighthouse beacon—a predictable “pulse” that astronomers regularly observe with radio telescopes. Although scientists can measure time with significantly lower accuracy using pulsars than with atomic clocks, the stars would not require calibration as degrading clocks would, providing stability for centuries.

While it’s interesting to consider whether the moon would have multiple time zones like Earth, NASA “does not currently see a use case for multiple time zones on the moon,” Coltre says.

We use 24 time zones spaced one hour apart, which are adopted to regulate day and night globally based on the Earth’s rotation. A day on the moon lasts two Earth weeks, meaning astronauts invariably have to sleep part of local days and work during local nights, making different time zones redundant, Heymans says.

Although these problems are technical in nature, they represent a paradigm shift in timekeeping, which has made a leap from tracking the sun and stars, and then relying on clocks, to now introducing the same technology beyond Earth.

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