Artist’s impression of astronauts working on the moon. Image source: NASA.
By the end of this decade, the moon will be buzzing with activity. Our nearest celestial neighbor will witness the arrival of the first astronauts since the Apollo era more than half a century ago. Multiple nations will place dozens of robotic explorers on and around it, vying for permanent bases on its dark, pockmarked surface. As the renaissance of the moon race draws ever closer, scientists are just beginning to address a key question: What time is it on the moon?
It turns out that this simple question has a complicated answer. So far, lunar exploration missions have been carried out according to the time of their respective countries. However, early last year, the European Space Agency (ESA) deemed the system unsustainable for upcoming lunar missions.
Without a lunar standard time, there is a risk of serious errors, says astrophysicist Catherine Heymans of the University of Edinburgh in the United Kingdom. Multiple spacecraft from different countries are expected to fly on or around the moon simultaneously, highlighting the need for common lunar time and further the need for a navigation system that facilitates real-time communications, collision avoidance and joint operations, according to European Space Agency.
On April 2, more than a year after ESA discovered the problem, the White House directed NASA to establish a new standardized lunar time by the end of 2026. Steve Welby, deputy director for national security at the Office of Science and Technology Policy, said in a statement on April 2.
Heymans said the White House’s intervention was very helpful because it really accelerated the plan to make it happen ahead of Artemis’ planned landing in late 2026.
Additionally, creating the moon’s own GPS requires consistent lunar time, Welby said. Currently, scientists rely on a network of radio antennas to ping the spacecraft regularly and time the time it takes for the spacecraft to return a ping, allowing scientists to zero in on its position. However, the Lunar Global Navigation Satellite System (GNSS), a constellation of small satellites that space agencies hope to complete by 2030, could provide better location tracking much like GPS provides time to smartphones and in-car maps on Earth. Same as location data.
moon timing
For us earthlings, time does not change. Even when you’re super bored and time feels like it’s passing extremely slowly, seconds still tick by at the same rate per second, defined as 9,192,631,770 energy transitions within a cesium atom, a decades-long ultra-accurate method for universal timekeeping.
Time passes a little faster on the moon, whose gravity is only one-sixth that of Earth. For example, if you were to launch a clock from Earth and wait 50 years, the lunar clock would run one second faster than the clock on Earth, which would take 50 years to establish the offset.
Heymans said it feels like science fiction, but it’s not. This is a very solid prediction of general relativity, one of the best-tested theories we have that explains the structure of the universe.
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According to the theory of relativity proposed by Albert Einstein more than a century ago, atomic clocks placed in different gravitational fields will tick at different rates. The same is true for astronauts aboard the International Space Station, but their orbits are close enough to Earth that they can calibrate their clocks to Earth’s Universal Coordinated Time (UTC). However, long-term human and robotic explorers staying on the moon will very slowly move away from their time on Earth. It’s a very, very subtle difference, Heymans said. Time is not absolute.
She added that such small differences would not cause trouble if there was only one astronaut working on the moon, in which case the changes would be easily explained. However, given the surge of interest in several countries, accurate time measurement has become even more necessary.
Julian Coltre, public affairs officer for NASA’s Space Operations Mission Directorate, said NASA’s proposed LTC time zone is a system that, while independent, still maintains traceability to Earth’s Coordinated Universal Time (UTC) to Facilitate seamless time transitions.
lunar timekeeper
It’s unclear how the space agency will determine time on the moon, with many technical details yet to be determined. An open question is whether lunar time should be maintained by placing atomic clocks on the moon, or synchronized with Earth, in which case a relay system would need to constantly communicate with our planet to record the time and send it Communicated to the lunar inhabitants.
Colter said it takes some research and planning, which is how the agency started the process. To understand how LTC relates to UTC, NASA may seek to conduct a clock demonstration mission on the lunar surface based on the atomic clocks flying on spacecraft today.
The weirdest idea of all is timing flashes from distant rotating stars called pulsars, extremely magnetized neutron stars born from the collapsed remnants of dead stars. As they rotate, electromagnetic radiation emitted from the magnetic poles flashes toward Earth like lighthouse beacons, predictable pulses that astronomers regularly observe with radio telescopes. Although scientists can measure time using pulsars with much less accuracy than atomic clocks, the stars don’t require calibration like degraded clocks, and therefore can provide stability for centuries.
Colter said that while it’s interesting to consider whether the moon would have multiple time zones like Earth, NASA doesn’t yet see a use case for multiple time zones on the moon.
We use 24 time zones, spaced one hour apart, to adjust global day and night based on the Earth’s rotation. A day on the moon lasts two Earth weeks, Heymans said, meaning astronauts always need to sleep during part of the local daytime and work during the local nighttime, without the need for different time zones.
While these problems are technical in nature, they represent a paradigm shift in the field of timekeeping, from tracking the sun and stars, then relying on clocks, to now building the same technology beyond Earth.
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Image Source : www.astronomy.com