Daylight Savings Time is upon us, but at least we’re not dealing with it on the Moon.
Agencies announced last week that they were working on giving the Moon its own time zone, and have been since November 2022, but that’s going to mean reckoning with politics, technology, and the physics of time itself. Here’s a look at how Lunar Standard Time might work and why it matters what time it is on the Moon.
A Tale as Old as Time (Zones)
We have 24 time zones here on Earth, dividing our planet into roughly 15-degree slices, which line up (again, very roughly) with how far our planet rotates in an hour. Those time zones were developed in 1883 in response to a new type of travel: trains.
Before 1883, most cities and towns ran on their own local time, which could vary by a few minutes from one city to the next. When it took days on horseback to get from one place to the next, that didn’t cause much of a problem. But once trains started zipping people from place to place in a matter of hours, things got more confusing.
“Due to this lack of time standardization, schedules on the same tracks often could not be coordinated, resulting in collisions. The major railroad companies as a result began to operate on a coordinated system of four time zones starting in 1883,” writes the U.S. Bureau of Transportation Statistics, the agency that’s now responsible for managing Daylight Savings Time.
140 years later, here we are again: a new way of traveling is forcing humanity to figure out how to standardize timekeeping. Thanks to space travel, we now have to reckon with timekeeping on other worlds whose rotation doesn’t match Earth’s. That’s why NASA, the European Space Agency, and other organizations from around the world are now actively working on establishing an official time zone for the Moon. But in some ways, it’s really just a logical extension of the invention of time zones back in 1883 — nothing new under the Sun (or on the Moon).
What Times Is It in Space? Who Knows!
At the moment, most space missions operate based on the time zone of their home country, or they use something called “mission elapsed time,” which is a 24-hour schedule based on when the spacecraft launched. Crews on the International Space Station run on UTC, or Coordinated Universal Time, also called Greenwich Mean Time. And that works pretty well aboard the ISS, which orbits 250 miles above Earth’s surface.
The Moon complicates things, partly because it’s so far away — but also because time literally works differently there.
Thanks to general relativity, which explains how massive objects affect space-time, time actually passes more slowly in a stronger gravitational field, and faster in a weaker one. Because the Moon is considerably smaller than Earth, its gravity is only about 17 percent as strong, and a clock running on the Moon pulls 56 microseconds ahead of Earth time every (Earth) day.
A 56-microsecond time difference sounds like something you could safely ignore, but those microseconds eventually pile up — and they can wreak havoc on the navigation systems that future astronauts and robotic rovers will use to find their way around the Moon. Both NASA and ESA are developing their own lunar versions of the GPS system we use on Earth. Lunar GPS, just like Earth GPS, will depend on ultra-precise measurements of how long it takes a signal to travel from a satellite to the ground. Microseconds will matter, unless you want to find yourself lost in Mare Imbrium and running low on oxygen.
A standard lunar time zone would also make it easier for missions from different countries to coordinate, something that’s becoming increasingly important as more national space agencies and private companies show an interest in exploring — or exploiting — the Moon. At least that’s the argument from ESA, NASA, and other agencies.
“Timing is critical for communications and navigation that will be needed for all activities on and around the Moon,” NASA representative Joshua Finch tells Inverse.
One Time Zone, Several Clocks
How would a lunar time zone work? That’s what space agencies and metrologists (scientists who specialize in measurements, including ways of measuring time) are working on right now.
One option could involve installing one or more “master clocks” on the Moon, either on the surface or in orbit, and letting the Moon literally run on its own (slightly faster) time. That gets a little finicky because lunar time runs ever-so-slightly differently depending on altitude and even latitude, so Lunar Standard Time may end up being an average of three or more atomic clocks at different places on the Moon.
That would require people (or more likely computers) here on Earth to keep track of the ever-shifting time difference between Earth and the Moon, but it would also make very good sense for operations on the Moon. Another option would involve basing lunar time on UTC, which means the Moon would basically be importing its time from atomic clocks on Earth — or else constantly “correcting” the slightly faster time on the Moon to bring into line with UTC.
But why is everyone talking about a single time zone for the entire Moon? That’s because the Moon rotates so slowly that it doesn’t make sense to divide it up into slices to mark time of day. Here on Earth, a day is just under 24 hours long, hence our 24 time zones. On the Moon, a day is just under 30 times longer. We track a lunar “day,” one complete rotation, by the “phases” of the Moon visible from Earth every month.
Living on Lunar Standard Time
No matter how we divide up time on the Moon, a lunar astronaut’s statutory “day” is never going to have any relation to the actual rotation of the body they’re standing on, or the actual cycles of dark and light overhead.
“Time zones on the moon probably are irrelevant for human physiology,” Erin Flynn-Evans, director of NASA's Fatigue Countermeasures Laboratory, tells Inverse. “When it comes to Circadian rhythms, all we really need is a 24-hour-ish schedule that we adhere to on a regular basis, with consistent light and dark. And when we don't have that, we have to create it.”
When Artemis III’s crew lands near the Moon’s South Pole sometime in 2025 or 2026, they’ll find themselves in surreal permanent daylight.
“The Sun will just kind of move around the horizon. I wish I could experience that, because it sounds so interesting,” says Flynn-Evans. “It’s not going to go up in the sky like it does on Earth; it’s just going to kind of circle the horizon, so most of the time it will be constant light.” Artemis III’s crew will rely on heavy-duty window shades and a firm schedule imposed by Mission Control to keep themselves tethered to a 24-hour day.
Astronauts aboard ISS already grapple with this, of course, but in the opposite direction — aboard the ISS, whizzing around the Earth at 17,000 miles an hour, the Sun rises and sets every 90 minutes.
So no matter what, astronauts’ Circadian cycles are always going to be at the mercy of artificial ways of relating to their environments, like clocks and station lighting — and at least for the foreseeable future, we Earthlings will always be tied to a roughly 24-hour day, because that’s written into our genes.
What About Mars?
In some ways, time will be easier to grapple with on Mars, where the actual day is 24 hours and 39 minutes long.
But despite the similarity, it’s going to be hard for "early birds" — the people whose internal clocks naturally want to run on a slightly shorter than 24-hour cycle — to stretch their Circadian cycles to match longer Martian days, while "night owls" might have an easier time of it.
"What we're doing to prepare for Mars is studying people on Earth who have to work on Mars time," says Flynn-Evans. "For each of our, you know, rover expeditions and lander expeditions to Mars, the scientists and engineers who work on those projects typically have to live on Mars time on Earth."
During the Phoenix Mars Lander mission in 2008, Flynn-Evans and her team studied 20 people working on "Mars time." They gave the lander crews blue light boxes to use at their workstations. Our eyes are more sensitive to blue light than to red, and Martian daylight has a distinctly reddish hue.
"So our thinking was if we give the scientists and engineers who are living on Mars time an enhanced blue light condition, then that will help them better adapt. And we found that the majority of people did," says Flynn-Evans. About 19 of 20 people on the project successfully adjusted to longer Martian days with a little help from blue lights. Similar measures might help future Mars explorers adjust, too.
And while the Moon will probably end up with just one time zone, Mars will likely end up with 24 or 25. Like Earth, Mars rotates fast enough that the Sun moves overhead about 14.5 degrees every hour — which means it’s definitely a different time of day at Gale Crater than on the eastern flank of Olympus Mons, for example. So future Mars will probably have its own set of time zones very similar to the ones here on Earth.
