THE JOURNAL
Artist’s impression of The Lunar Gateway in orbit around the moon in 2024. Image courtesy of Mr Alberto Bertolin/Nasa
Call it a moonshot for timekeeping. After half a century in which we have been content to leave lunar exploration to robots and during which we have become entranced by the idea of putting a person on Mars, the world’s space agencies and rocket-obsessed billionaires have returned to the idea of manned moon visits. The next generation of lunar astronauts is likely to spend longer on the moon and future missions are more likely to be the product of international co-operation. In the words of the European Space Agency (ESA), “accurate navigation demands rigorous timekeeping”. In other words, if everyone’s not on the same page, things could all go a bit Apollo 13. But what about the actual mechanics of telling the time on our celestial companion? Best strap yourself in…
Astronauts have watches. What’s the problem?
Indeed they do. They probably have a few computers involved as well, just in case the mechanical watches don’t cut the mustard. The problem is that each space agency and corporation uses its own native, Earth-based time zone for its missions, both in terms of the astronauts’ onboard timekeeping and for their communication and navigation. This, says the ESA, will not be sustainable. It is calling for an international body to establish proper lunar time zones, like the ones on Earth (which have been around since 1884, since you ask).
All right. Draw 24 lines around the moon and call it a day. Problem solved.
Not quite. First, who says there should be 24? Our model of timekeeping – 24 hours a day, 60 minutes an hour, 60 seconds a minute – derives from ancient Egyptian and Greek calculations, built up over hundreds of years at a time when the most accurate clocks used buckets of water and the typical point of reference was a sundial. It’s all a bit rough and ready – not words you happily associate with space flight. (The adoption of 12 hours of day and night might, however, relate to the 12 lunar months in a year. We’ll be hearing more about them later.) Mankind has never had the chance to lay down the rules for telling the time on a new celestial body and there might be a more logical way of doing it. We Brits would appreciate it if the end result could be known as Greenwich Moon Time, but before we get to all that, there’s a bigger problem with imposing the terrestrial model of 24-hour days on the moon.
“Mankind has never had the chance to lay down the rules for telling the time on a new celestial body and there might be a more logical way of doing it”
Which is?
A lunar day is 29.5 Earth days long, otherwise known as a lunar month. Because, unlike the Earth, the moon doesn’t rotate on its own axis – it’s tidally locked, so we always see the same side. So, the passage of sunlight across the moon’s surface is slower because it rotates around the Earth (and by extension, the Sun). We see this as the waxing and waning of the moon, from crescent to full moon and back, but to someone on the moon’s surface, it would be experienced as a two-week daytime followed by two (Earth) weeks of darkness. Obviously, a method of timekeeping that aligns with both human sleep patterns and lunar cycles will be needed. And if you’re meeting someone at the Sea of Tranquillity for lunch, bring snacks.
It sounds complicated. Are Switzerland’s finest minds on the case?
This isn’t the half of it. Clocks run faster on the moon than on Earth due to its lower gravitational pull, so over time your funky new moon clock will fall out of sync with Earth time. Only by 56 millionths of a second a day, but for precision systems such as GPS, that kind of difference can soon become a problem. If there are Swiss brains applying themselves to the issue, they’re more likely to be found at Cern than in Geneva’s watch factories. There is one mechanical watchmaking invention that might be about to come into its own, though.
Don’t tell us the humble world of gears and springs has been sitting on the answer the whole time?
Perhaps. Certainly for the off-duty moon dweller, there is a ready-made solution to those long lunar days – and it lets you keep track of time back home as well. Ladies and gentlemen, the moon-phase watch. Hitherto one of the least practically useful additions to a mechanical watch, these stylised displays give you an at-a-glance measure of the moon’s 29.5 day cycle. For earthly collectors, they’re a romantic, whimsical touch that nods to the ancient origins of timekeeping. But for our men and women bouncing gracefully sur la lune, they become a useful instrument like never before. All that’s needed is for Swiss watchmakers to blow up the size of the moon-phase display, add some kind of numerical scale around the edge for easy reference and hey presto. If it has a calendar function built in, you’ll know when it’s convenient to call home to say goodnight. The lunar sunset will last a full Earth day, after all.