Daylight saving time is upon us, but at least we’re not dealing with it on the moon.
Agencies announced last week that they are working to give the moon its own time zone, and have been since November 2022, but that will 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 discs that correspond (again, very roughly) to how far our planet rotates in an hour. These time zones were developed in 1883 in response to a new mode of travel: trains.
Before 1883, most cities and towns ran their own local time, which could vary by a few minutes from one city to the next. If it took days to get from one place to another on horseback, that wasn’t a big problem. But when trains started taking people from place to place in a matter of hours, things got more confusing.
“Due to this lack of time standardization, timetables on the same tracks often could not be coordinated, which led to collisions. The major railroad companies therefore began operating under a coordinated system of four time zones beginning in 1883,” writes the US Bureau of Transportation Statistics, the agency now responsible for administering daylight saving time.
140 years later, here we are again: A new way of travel is forcing humanity to figure out how to standardize timekeeping. Thanks to space travel, we now have to deal with the measurement of time on other worlds whose rotation does not correspond to that of Earth. Because of this, NASA, the European Space Agency, and other organizations from around the world are now actively working to establish an official time zone for the moon. But in a way it’s really just a logical extension of the invention of time zones in 1883 – nothing new under the sun (or on the moon).
What time is it in space? Who knows!
Right now, most space missions operate based on their home country’s time zone or they use something called “mission elapsed time,” which is a 24-hour schedule based on the spacecraft’s launch. The crews of the International Space Station work according to UTC or Coordinated Universal Time, also known as Greenwich Mean Time. And that works pretty well aboard the ISS, which is orbiting 250 miles above the 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 spacetime, time actually passes more slowly in a stronger gravitational field and faster in a weaker one. Because the moon is significantly smaller than earth, its gravity is only about 17 percent as strong, and a clock running on the moon is 56 microseconds ahead of earth time every (earth) day.
A time difference of 56 microseconds sounds like something you could safely ignore, but those microseconds eventually add up — and they can wreak havoc on the navigation systems that future astronauts and robotic rovers will use to navigate the moon. Both NASA and ESA are developing their own lunar versions of the GPS system we use on Earth. Lunar GPS, like Earth GPS, depends on ultra-precise measurements of how long it takes for a signal to travel from a satellite to the ground. Microseconds matter, unless you want to lose yourself in Mare Imbrium and be low on oxygen.
A standard lunar time zone would also make it easier for missions from different countries to coordinate, which is becoming increasingly important as more national space agencies and private companies show interest in exploring — or exploiting — the moon. At least that is the argument of ESA, NASA and other agencies.
“Timing is critical to the communications and navigation required for all activity on and around the moon,” said NASA representative Joshua Finch The opposite.
One time zone, multiple clocks
How would a lunar time zone work? Space agencies and metrologists (scientists specializing in measurements, including methods of measuring time) are currently working on this.
One option might be to install one or more “master clocks” on the moon, either on the surface or in orbit, and literally have the moon run by its own (slightly faster) time. This gets a little finicky because lunar time varies very slightly with altitude and even latitude, so lunar standard time can average three or more atomic clocks in different locations on the moon.
That would require humans (or more likely computers) here on Earth to keep track of the ever-changing time difference between Earth and the Moon, but it would also make a lot of sense for operations on the Moon. Another option would be to base lunar time on UTC, which means the moon would essentially import its time from atomic clocks on Earth – or else would constantly “correct” the slightly faster time on the moon to match UTC in to reconcile.
But why is everyone talking about a single time zone for the entire moon? That’s because the moon rotates so slowly that dividing it into slices to mark the time of day doesn’t make sense. Here on earth, a day is almost 24 hours long, hence our 24 time zones. A day on the moon lasts almost 30 times longer. We track a lunar “day,” one complete revolution, by the “phases” of the moon that are visible from Earth each month.
Life according to lunar standard time
No matter how we divide time on the moon, a lunar astronaut’s prescribed “day” will never bear any relation to the actual rotation of the body on which he stands, or to the actual cycles of dark and light overhead.
“Time zones on the moon are probably irrelevant to human physiology,” says Erin Flynn-Evans, director of NASA’s Fatigue Countermeasures Laboratory The opposite. “When it comes to circadian rhythms, all we really need is a 24-hour schedule that we stick to on a regular basis, with consistent light and dark. And if we don’t have that, we have to make it.”
When the crew of the Artemis III lands near the moon’s south pole sometime in 2025 or 2026, they will find themselves in surreal, perpetual daylight.
“The sun will just move around the horizon. I wish I could experience that because it sounds so interesting,” says Flynn-Evans. “It will not rise to heaven as it does on earth; it will simply orbit the horizon, so it will be constant light most of the time.” The crew of the Artemis III will rely on sturdy blinds and a fixed schedule imposed by Mission Control to adapt to a 24-hour day to keep.
Astronauts aboard the ISS are already struggling with this, of course, but in the opposite direction — aboard the ISS, whizzing around the Earth at 17,000 miles per hour, the sun rises and sets every 90 minutes.
No matter what, astronauts’ circadian cycles will always be at the mercy of artificial ways of relating to their surroundings, such as clocks and station lights — and for the foreseeable future, at least, we Earthlings will always be locked into a roughly 24-hour day, because that’s in written into our genes.
What about Mars?
In a way, time will be easier to manage on Mars, where the actual day is 24 hours and 39 minutes.
But despite the similarity, “early risers” — the people whose internal clocks naturally want to run on a slightly shorter than 24-hour cycle — will find it difficult to stretch their circadian cycles to accommodate longer Martian days, while “night owls “Maybe it’s easier for you.
“What we’re doing to prepare for Mars is studying people on Earth who have to work in Martian time,” says Flynn-Evans. “For each of our rover expeditions and lander expeditions to Mars, the scientists and engineers working on these projects usually have to live on Earth on Mars.”
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 lightboxes to use at their workstations. Our eyes are more sensitive to blue light than red, and daylight on Mars has a distinctly reddish tint.
“So we thought if we gave the scientists and engineers who live on Mars an improved blue light condition, it would help them adapt better. And we found that the majority of people did,” says Flynn-Evans. About 19 out of 20 people on the project have successfully acclimated to longer Martian days with a little help from blue lights. Similar measures could also help future Mars explorers adapt.
And while the moon will likely only have one time zone, Mars will likely have 24 or 25. Like Earth, Mars spins fast enough that the Sun moves about 14.5 degrees overhead every hour – meaning it’s definitely a different time of day at Gale Crater than, say, on the east flank of Olympus Mons . So future Mars will likely have its own time zones very similar to those here on Earth.