How to keep track of time in space, William Shatner’s new mystery series, The UnXplained premiers this month, and a couple of sightings from one of our listeners.

The Question

In the movie, Edge of Tomorrow, aliens are able to manipulate time by forcing humans to relive the same day. If aliens are able to manipulate time, do you think it would be localized or would it affect all of space-time?

News

How Should Space Settlers Keep Track of Time?

We appear to be on the cusp of an era where humans live outside this pale blue dot. According to some newly leaked NASA documents, the agency hopes to build a moon base by 2028.

There are serious technical hurdles to establishing space settlements and enduring long-term flights: How will humans grow food? What happens to our waste? But there are also squishier, logistical ones that we take for granted here on Earth. One of the first things we’ll need to figure out is how to keep track of time.

The solution might seem straightforward: just bring a watch and a calendar, and mark off the days! And yes, this is how the only full-time space settlement—the International Space Station—handles things. The crew of the ISS operates on Greenwich Mean Time and, via their close contact with Earth, gets updates on the time.

GMT For Space

But there are challenges to keeping space dwellers on an Earth-bound time-keeping system. One is the practicality of using a time-keeping system that ignores your local reality. Keeping astronauts on a 24-hour, GMT-based system makes things easier for ground control, but trying to keep Earth hours takes a toll on astronauts’ sleep, as their circadian rhythms are thrown off by the comparatively erratic light cycle: The ISS orbits Earth every 90 minutes, so over the course of a typical 24-hour Earth “day,” the crew sees 16 sunrises and sunsets.

Astronomers, science-fiction writers, and enthusiastic hobbyists have presented a range of proposals for new time-keeping systems for potential space settlements. Mars has particular intrigue to those dreaming of space settlements. Thomas Gangale, creator of the Darian calendar, came up with his design in 1985. “If we’re going to send people to Mars and settle it, they’ll need to reckon time according to the natural rhythms of the planet,” Gangale says. His system adapts our traditional Earth time-keeping methods to the rotation and solar orbit of Mars. While Earth rotates once every 23 hours and 56 minutes, Mars’ rotation is slightly longer: A Martian day is just shy of 24 hours and 40 minutes, a unit astronomers call a sol. Mars’ solar orbit is about twice as long as Earth’s: It takes 687 Earth days to our 365, which comes to 668 sols.

What's In A Day

We could just leave time measurement at the sol level, and in fact, some Mars calendar proposals suggest that. On Earth, the Julian calendar assigns each Earth day a number, counting up from Jan. 1, 4713 B.C., as “Day 0,” which makes it easier to calculate day-based milestones like use-by dates for food. A Mars sol-based calendar would work similarly, counting up from a “Day 0” we’d need to decide on.

Currently, engineers take care of this issue by translating between precise Earth time and the spacecraft’s USO time readings. But as we get deeper into space or need to perform more instantaneous maneuvers, depending on Earth time would quickly become cumbersome.