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Time passes faster on the moon. Now we know exactly by how much.: ScienceAlert

Time passes faster on the moon. Now we know exactly by how much.: ScienceAlert
Time passes faster on the moon. Now we know exactly by how much.: ScienceAlert

Since astronauts last left the lunar surface Time passed 52 years ago. Compared to us on Earth, the moon waited just a little longer for our return – about 1.1 seconds.

That doesn’t sound like much, nor does the 57 millionths (0.0000575) of a second by which the lunar time increases every day compared to that of our home planet.

But this crucial finding from a new study by NASA scientists could make all the difference in synchronizing navigation systems as the U.S. space agency launches its long-awaited manned missions to the moon and beyond.

We have known since Albert Einstein’s general theory of relativity that gravity can slow down time. But the practical possibilities for measuring temporal distortions associated with differences in gravity – such as the contrast between the gravitational pull of the Earth and that of the Moon – lag far behind.

It is only in the last decade or so that atomic clocks have been available that are sensitive enough to detect small time differences between two objects that are moving relative to each other or are subject to different gravitational forces.

And since there was a half-century gap between manned moon landings, scientists had no pressing need to figure out how these tiny time differences between Earth and our moon affected things. The moon has one-sixth of Earth’s gravity, but astronauts only stayed on it for short periods of time, so this wasn’t a big problem.

Now scientists have set a deadline: NASA wants to return astronauts to the moon by 2026 as part of its Artemis missions to begin exploring possible locations for lunar bases that could one day serve as a stepping stone to Mars.

“We expect a permanent presence on the moon,” Cheryl Gramling, a navigation system engineer at the Goddard Space Flight Center in Maryland, told New scientific magazine Jonathan O’Callaghan.

“Earth-based infrastructure like GPS provides time accuracy down to the nanosecond,” Gramling continued. “When you’re trying to navigate or land on the moon while avoiding dangerous areas, that precision is important.”

Earlier this year, in April, NASA and other U.S. agencies were tasked with developing a unified time reference system for the Moon that other space agencies could agree on.

This new discovery helps in that regard and has been in the works for some time. Slava Turyshev, a physicist at NASA’s Jet Propulsion Laboratory who led the study, told O’Callaghan, “Someone had to sit down and do the calculation.”

Seen from Earth, the Moon appears to gain 57 millionths of a second per Earth day. Turyshev and his colleagues arrived at this figure by calculating the sliding time scale for the Earth and the Moon relative to the barycenter of the solar system. This is the common center of gravity of the solar system around which the Sun, planets and satellites orbit in a delicate balance.

Turyshev and his colleagues’ calculations are very close to the 56.02 microseconds determined in February by another team of researchers at the U.S. National Institute of Standards and Technology. But over such large distances, tiny fractions of a second matter, so there is still work to be done.

None of the results have been peer-reviewed, and the final definition of lunar time must be confirmed by a number of authorities and international bodies, such as the International Bureau of Weights and Measures and the International Astronomical Union, which plan to meet in August.

We also need to keep in mind how the rotation of our planet Earth is strangely slowing down, making our days a little longer – and how human exploitation of the Earth is changing its rotation.

The study was published in arXiv Preprint server before peer review.

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