A Lunar time zone? Here's why telling time in space is tricky Scientists are pondering how to tell time on other celestial bodies. It's a lot harder than you might think.

If daylight saving time seems tricky, try figuring out the time on the moon

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The clock leaped ahead last night, and that may have left you a little confused about what time it is this morning. But scientists say this is just a small taste of the confusion that's coming when humans start traveling into space. Away from planet Earth, time gets more complicated, and that's why the European Space Agency is now proposing to create a new time standard for the moon. Joining me to discuss what this means is NPR science correspondent Geoff Brumfiel. Welcome to the program.

GEOFF BRUMFIEL, BYLINE: Hi, Ayesha. Nice to be here.

RASCOE: Yes. OK. So Geoff, what time is it on the moon right now?

BRUMFIEL: That's an excellent question. So a day on the moon is defined by the time it takes the sun to get to the same point in the sky - is 29 1/2 Earth days. So that's actually not a practical way to do time on the moon. The way all the rovers and probes and things we have up there right now work, they just work off Earth time. But the thing is, there's plans afoot to do a lot more with the moon - send a lot more missions, start sending crewed missions over there. NASA wants to send astronauts to orbit the moon as soon as next year. And that's the first step, they hope, to putting a space station around the moon and eventually getting a permanent settlement on its surface. And these scientists say that, you know, if we're going to do all that, we're going to need a new kind of time. We're going to need lunar time.

RASCOE: Why couldn't they just bring a watch, bring a cell phone, and they would know, like, what time it is? That's how we figure out time here.

BRUMFIEL: Exactly. Well, you know, I called Javier Ventura-Traveset at the European Space Agency, and he told me that's actually how the original Apollo missions did it. And it kind of made sense - right? - because they were the only ones up there. It didn't really matter what time it was.

JAVIER VENTURA-TRAVESET: It is only one user. So you could conceptually think, OK, I have my own clock in my mission, and I am connecting with the Earth to align my clock with the clock of the Earth.

BRUMFIEL: But here's the thing you really need to know about time, Ayesha - is that its true power comes from multiple people agreeing on the time. And so when you're the only ones up there, you can just work with Earth time. But imagine there's a bunch of robotic spacecraft flying around. There's, you know, rovers on the surface and astronauts, and they all need to agree on the time to work together.

RASCOE: So what are we talking about, then? Would there be a new time zone for the moon?

BRUMFIEL: So we're actually talking about something much more fundamental, which is a new time scale. So here on Earth, we all have our time zones, but there's actually a single time standard. It's called Coordinated Universal Time or UTC. Maybe you've heard of that.

RASCOE: I've heard of that, but I don't know much about it.

BRUMFIEL: UTC - the way it works is it sort of synchronizes all the seconds and minutes and hours, and then we all set our own time zones. It keeps the internet humming. It's responsible for cell phones being able to talk to each other over networks, financial markets. But most importantly, it's really key to navigation. And now imagine we're trying to extend UTC to the moon.

So there's a few problems with taking our time scale and moving it to the moon. The first is that Earth is a little over a light second away from the moon. That means if you're broadcasting a time signal from Earth, it'll arrive a little late. That's not a huge deal at all. You could just tweak your clocks, but it does kind of complicate things. But there's a second, really, really weird thing that happens. Time actually flows differently on the moon than the Earth. So Ventura-Traveset said, imagine taking two clocks and putting one on the Earth and one on the moon.

VENTURA-TRAVESET: And then you say, OK, both are exactly at the same time now. And then you let them run. And after 24 hours, they don't have the same time.

BRUMFIEL: It's not that one is ticking differently because it's on the moon. It's because time is literally flowing faster on the moon than it is on the Earth.

RASCOE: That is very - that is strange.

BRUMFIEL: Now, it's only about 56 microseconds every day. That's nothing for humans. But 56 microseconds makes a big difference when you're talking about navigation or communication or electronics. And so it does matter for all these systems that we want to build on the moon. So defining any time scale takes a long time, and it's going to take a lot of discussions between all the space agencies and people here on Earth in coming months and years.

RASCOE: That's NPR science correspondent Geoff Brumfiel. Thank you so much.

BRUMFIEL: Thank you, Ayesha.

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