Of the many fantastic ramifications of Einstein’s brilliant Theory of General Relativity, one of the most mind-boggling things is how gravity affects time. The stronger an object’s gravity, the more time is stretched, making it pass more slowly. This means that if you were to visit a planet with a mass greater than Earth’s, time would tick slightly slower. In fact, the same things applies to different elevations — time passes slightly slower at the beach than at the peak of Mt. Everest. This is because gravity has a stronger effect closer to the center of the Earth.
Conversely, time goes faster relative to Earth on a less massive cosmic body. For instance, that’s exactly what happens on the Moon.
Lunar Time
Although Albert Einstein introduced us to gravity’s influence on time more than a century ago, measuring such minuscule temporal distortions has only recently become feasible with advanced atomic clocks. These clocks can detect small time variations between objects moving differently or experiencing distinct gravitational forces.
According to new research from NASA scientists, time on the Moon runs faster than on Earth by a mere 57 millionths of a second per day. To put things into perspective, in the 52 years since astronauts last set foot on the Moon, time there extended by roughly 1.1 seconds compared to Earth.
At a glance, this time difference may seem trivial and insignificant. But it could make all the difference during sensitive missions where navigational systems need to be in perfect sync. As NASA prepares for its Artemis missions aiming to return astronauts to the Moon by 2026, understanding and managing these time differences has never been more important.
In anticipation of upcoming manned missions to the Moon, NASA now wants to develop a new “time scale” on the moon. Others have called it a “time zone” for the moon but that’s not precisely correct. This system of measurement is supposed to account for the slight discrepancy in how time passes between the two cosmic bodies.
A recent memo from the White House also directed NASA to map out its plans for this new time scale by December 31, calling it “foundational” to renewed US efforts to explore the lunar surface. NASA is tasked with implementing such a system no later than the end of 2026 — or at least before the launch of the first Artemis mission.
Time dilation and atomic clocks
This most recent precise measurement of the time dilation effect on the Moon should help with these efforts. Physicists at the Jet Propulsion Laboratory led by Slava Turyshev arrived at the 57 microseconds figure by computing the sliding scale of time for the Earth-Moon system relative to the Solar System’s common center of mass.
However, earlier research by the US National Institute of Standards and Technology found the relative difference in time stretching was 56.02 microseconds. Since neither result has been peer-reviewed, the jury is still out on the final value for lunar time.
There are also plans to install atomic clocks on the moon’s surface. In the initial phase, NASA would first like to use atomic clocks inside satellites that orbit the moon. An atomic clock uses the vibrations of atoms, typically cesium or rubidium, to measure time with exceptional accuracy. A network of clocks on the moon could work in concert to inform the new lunar time scale, just as atomic clocks do for the Universal Time Zone (UTC) on Earth.
The new time scale would underpin an entire lunar network, which NASA and its allies have dubbed LunaNet.
“You can think of LunaNet like the internet — or the internet and a global navigation satellite system all combined,” Cheryl Gramling, the lunar position, navigation, and timing and standards lead at NASA’s Goddard Space Flight Center in Maryland, told CNN. It’s “a framework of standards that contributors to LunaNet (such as NASA or the European Space Agency) would follow.”
“And you can think of the contributors maybe as your internet service provider,” Gramling added.
