What time is it? OK, fine, what time is it on the Moon? The Moon orbits the Earth, so it doesn’t fall into a specific time zone. Also, there’s lower gravity on the surface of the Moon, which changes the rate that clocks tick. Well… It’s time to introduce Lunar Time.
Show Notes
- The Necessity for Lunar Timekeeping
- Challenges in Defining Lunar Time
- Absence of Natural Time Zones
- Gravitational Time Dilation
- Proposed Solutions:
- Lunar Coordinated Time (LCT)
- Synchronization with Earth Time
- Implications for Future Missions:
- Navigation and Operations
- Interoperability
Transcript
AstroCast-20250217
Transcribed by TurboScribe.ai. Go Unlimited to remove this message.
[Fraser Cain]
AstronomyCast, Episode 744, Lunar Time. Welcome to AstronomyCast, your weekly facts-based journey through the cosmos, where we help you understand not only what we know, but how we know what we know. I’m Fraser Cain, I’m the publisher of Universe Today.
With me as always is Dr. Pamela Gay, a senior scientist for the Planetary Science Institute and the director of Cosmic Quest. Hey Pamela, how are you doing?
[Dr. Pamela Gay]
I am doing mostly well. I rebooted my computer and it lost its brain, which caused me to lose my brain, but I think all brains have now been gathered up.
[Fraser Cain]
I think the fact that we have been wrestling with audio, software, hardware, codecs, gain, normalization, leveling for the entire length of time of AstronomyCast is hilarious. And I don’t mean that it’s been funny, I mean it’s been enraging. We have, like, why is this a problem?
Why is this happening? Why, after 18 years, can you not have a microphone connected to a computer that the sound goes into the microphone and is recorded by the computer and it’s fine? Like, is that too much to ask?
It is. It is. So this is what we get.
And this is what you get, which is us having hardware, software, audio devices betray us. And you, the listener, together.
[Dr. Pamela Gay]
The thing that gets me at the most stupid level is they have now added rainbow LEDs to every single piece of technology, and they can get all those rainbow LEDs to sync with this, that, and the other thing to display brand colors, to display whatever the heck you want. Light, in terms of making things look rainbow of your choice, they got it. Lighting of green screens, hard.
Audio. Audio is impossible.
[Fraser Cain]
Impossible. Can’t be done. Anyone who’s going to try to do audio, you’re out of your mind.
It’s, it is just, there’s no way that anyone can record audio from a microphone onto a computer and have that be saved. Like that’s, that’s rocket science. Alright.
What time is it? Okay, fine. What time is it on the Moon?
The Moon orbits the Earth, so it doesn’t fall into a specific time zone. Also, there’s lower gravity on the surface of the Moon, which changes the rate the clocks tick. Well, it’s time to introduce Lunar Time.
And we will talk about it in a second, but it’s time for a break. And we’re back. Alright, so when did the, I guess, the international space exploration community realize that there is a problem with thinking about time on the Moon?
[Dr. Pamela Gay]
So there’s always been this, yeah, we need to worry about this. This concern going on, like even during the Apollo missions, they had insane amounts of updating of the clocks to make sure they could figure out how fast they were going in feet per second, to figure out where they were, to figure out all sorts of different things that you don’t realize require you to know when you are. And since we didn’t stay on the Moon, it didn’t stay a problem and it kind of fell by the wayside because there are a lot of problems in space science that need solutions and that one could just wait.
But in the early 2020s, as it became clear that a new Moon race was on, as it became clear we were and are going back, some of us, someday, some combination. It started with ESA being like, okay, we need to start defining this. We need to start figuring this out.
And so ESA started putting together working groups in 2023 and not to be outdone. In April of 2024, the White House put out a memo that is no longer available on the Internet. Gripe of the day.
[Fraser Cain]
That’s really helpful for doing research, background research on this. It’s fine, we’ll just go with what the Europeans say.
[Dr. Pamela Gay]
There are so many points of information that no longer can be found. But anyways, moving on to discuss the reality of the situation. So it was realized we need to define this.
And the White House in April of 2024 said, NASA, you do you, coordinate with whomever you need to coordinate with. And by 2026, we want a Lunar Coordinated Time. This is because everything gets gets abbreviated stupid.
It’s called Coordinated Lunar Time and it is abbreviated LTC, which is consistent with Coordinated Universal Time, which is UTC.
[Fraser Cain]
Okay, so we’ve got Lunar Coordinated Time. And what is the proposal for Lunar Coordinated Time? What what will it be?
[Dr. Pamela Gay]
Well, and this is where it gets, what is the problem that we have to solve is the starting point. So for instance, why is it that when astronauts go to the moon, they can’t just use Houston time, which is pretty much what the Apollo astronauts did. Why can’t we in general just sync our clocks with the clocks on Earth and move on with life?
And the problem’s relativity. So in the initial, what does this need to entail? They identified it has to have traceability back to UTC.
It has to have accuracy for navigation and science, and it has to be scalable beyond the Earth moon. And all of this means we need to define all the parts of the equations that cause time to speed up and slow down based on the size of the gravity well you’re in and how fast you’re moving.
[Fraser Cain]
Right.
[Dr. Pamela Gay]
And luckily, the moon’s motion is not the dominant factor. We can figure it out. It is getting thrown into the calculations.
It’s actually the difference in the mass between the moon and the Earth that creates the biggest problems that we have to be able to correct for. The Earth has a much bigger mass, which means that our aging is slower compared to people who are in orbit around us who are aging faster. Always think of the, um, I just forgot the name of the movie.
Oh, Interstellar. Yeah. Always, always think of Interstellar when you’re trying to remember who ages this.
[Fraser Cain]
Yeah, that’s true. That’s for me. That’s first principles is Interstellar.
Yes. Think back Interstellar. He spent a day near a supermassive black hole, and when he came away from the supermassive black hole, his daughter had experienced 40 years.
[Dr. Pamela Gay]
Yeah.
[Fraser Cain]
And so, um, and yeah, that clocks run more slowly near to higher gravity, gravitational wells.
[Dr. Pamela Gay]
And slower clocks means you age less. Faster clocks mean you age more just for people who need to get all of that straight in their head, which includes people like me.
[Fraser Cain]
Right. But the balance that you’re mentioning though, is it’s not just the fact that you are near a gravitational well, if you are farther away from the gravitational well, then the clocks are going to run more quickly for you. But then also there is the speed of your spacecraft relative to the person who is not.
And so you’ve got a spacecraft that it’s going and then it’s flipped in reverse.
[Dr. Pamela Gay]
Which the ISS has. So with the International Space Station, they’re going round and round at a zippy pace. And because they’re going at a zippy pace, they are aging slower than the people on the surface of the planet.
Here’s where you think of Ender’s Game.
[Fraser Cain]
Um, right.
[Dr. Pamela Gay]
I apparently do everything by movie reference.
[Fraser Cain]
No, I think that’s perfectly appropriate. And then in fact, there is a perfect balance point where the people who are in space, and I forget the altitude, but there’s a place where you will be the compared to a person on Earth, you’re experiencing less gravity. So your clock is clicking more quickly, but also you are moving faster.
And so your clock is clicking more slowly. And there is this perfect spot that you could be orbiting around the Earth and you wouldn’t experience any time drift with those two factors. But the point that I think, you know, back to what you’re saying, right?
That, that when you’re on the moon, the moon is going around the Earth. That when you’re orbiting around the moon, you were going at a certain velocity relative to the Earth. When you’re at a lunar halo orbit, you’re going a certain speed.
When you’re down on the surface of the planet, you’re experiencing different amounts of gravity and that the clocks are going to tick at a different time compared to a person on the surface of the Earth for every single one of those conditions.
[Dr. Pamela Gay]
Yeah. And, and this is where, uh, the white house in April of 2024 gave NASA until 2026 to figure this out.
[Fraser Cain]
Um, and you know what, I want to take a break before we figure out, like this is a cliffhanger. They were tasked to figure this out and what they discovered was, and we’ll be back in a second and we’re back. What did they figure out?
[Dr. Pamela Gay]
They figured out they being NIST, the national institutes for standards and technology figured out that it is when you do all the equations and you consider the orbital motion of the earth, the orbital motion of the moon. Um, it is the mass difference between the moon and the earth that dominates the difference in the equations of time between the two and not the speed, not the speed. It is not the speed that is the dominant factor.
And because of this, uh, there is, um, and here, I’m just going to read from a paper that came out in August of 2024, uh, from NIST, uh, the citations authors are Neil Ashby and Bunjanath Patla. Um, we estimate the rate of clocks on the moon using a locally freely falling reference frame, coincident with the center of mass of the earth moon system. A clock near the moon’s solenoid ticks faster than one near the earth’s geoid accumulating an extra 56.02 microseconds a day, which is a very, very, uh, fancy way of saying that at the surface of the moon compared to the surface of the earth, um, that, that clock is ticking faster. You are aging faster on the moon and it’s a small amount, but it’s amount that’s going to add up. And it’s an amount that if you don’t take it into account, once we start trying to develop a global positioning system for the moon, we won’t be able to do it. And the other thing is that as we start doing things like building telescopes on the moon and trying to coordinate data between lunar observations and earth based observations, if we don’t take into account this difference of 56.02 microseconds a day, our, our ability to align those, those data sets won’t be there. Um, so, so things that are affected, if you don’t take this into account, um, I mean, obviously pulsar timing, that’s super simple, uh, where things are is going to drift over time. If you don’t take it into account and you try using the exact same global positioning system, uh, equations that we use for our, not the equations are the same. If you start using the same values, uh, that we use for our earth system, um, it’s not going to work.
You’re going to have to update the chips that go in your phone and run the calculations to have the right constants. Um, one of the most amazing things that’s going to be totally different if you don’t take this into account is our ability to do interferometry at radio wavelengths. Cause right now we can have different radio observatories all over the world tied to their, their atomic clocks, taking observations with those timestamps inside the observations and using amazing computer systems.
We can shift the data around to align the incoming radio waves to create a radio dish. That’s the size of the earth. Now, when the radio waves are coming into the moon, we have to account for the difference in distance to the lunar dish and the earth dish.
That’s one thing that has to do in the process of aligning the data, but then we also have to either stretch or compress. And in this case, it turns out if, if time is, is going faster, you have to stretch the data out to get the time that’s passing to be the same for the data collected on the moon and the data collected on the earth. And that’s just wild to me to think about.
Time is going to affect things at that level.
[Fraser Cain]
Your hair again.
[Dr. Pamela Gay]
Okay. I’m looking for, I’m apparently going to use a booklet to hold back my hair. Perfect.
Rich, feel free to leave this in. So our audience knows what chaos is occurring when they get the audio file. I am very sorry, everyone.
I am going to have some housework done next week to seal the walls of my studio. And so I haven’t set my good mic back up after getting a computer, because I’m just going to have to move everything anyway. This is a high quality mic.
It’s just subject to long hair.
[Fraser Cain]
All right. We’re going to continue this conversation, but it is time for another break. And we’re back.
Um, right. So it’s, it’s kind of fascinating to think like the nitty gritty details. People are like, Oh, I want us to be living on Mars.
We want to be a, have a future solar system spanning civilization. But you can imagine somebody, you know, now detail has to show up and sort of join the conversation. And can you imagine taking that concept to the next level where you’re like, Oh, okay, what does it mean to be out at the L2 Lagrange point?
What does it mean to be on Mars on the surface of Mars in orbit around Mars on Phobos, uh, what time does Parker solar probe experience compared to the time that is experienced by us here on, on earth and that, that a future solar system spanning civilization, especially one that’s attempting to conduct science operations, trying to synchronize global positioning systems and communication systems to manage the time delays is going to just have a headache of the nth degree.
It’s mind bending. And, and yet you can see, yeah, if you don’t account for that, that time dilation, then you are not going to be able to align the measurements made by a interferometer that’s operating between the earth and the moon. You are not going to have an accurate timekeeping of when events happened so that you can make sure that the packets are arranged in the right way to put together a communication system.
Like all of these are actually going to be a big enough problem that the European space agency is assigning a group. NASA is assigning a group and they’re going to come together with some future global standards that then everybody, including the Chinese probably will have to work with. It’s, it’s a, it’s crazy.
It’s kind of humbling.
[Dr. Pamela Gay]
It’s not linear. I mean, this is the crazy thing because things are, are on elliptical orbits. The, the offset in time varies with time.
So you have to basically define, this is the moment at which clocks are synced. And now to figure out when this place is compared to when this place is, you have to take into account the overall offset due to mass, which is a standard. You have to, we assume the mass of the moon will remain constant.
It’s a good idea. But then you also have to take into account that yes, there is a subtle difference due to orbital speed that can mostly be ignored, but not completely be ignored. And the orbit’s an ellipse.
So the difference in the rate of time passage varies as a function of where you are in your orbit and the rate you’re going in your orbit. And, and this is something that you have to take into account for every world, for every different mass object. And you have to layer on the, I’m on Phobos, which means I’m in motion due to going around Mars, but I’m also in motion due to overall motion going around the sun.
And then you have to take into account the fact that when you’re looking at the signals, the time that it takes each successive wave getting to you is going to be different. So there’s a Doppler shifting of the signal. Now that doesn’t affect the rate of time that affects the rate of incoming information, but all of these things have to be taken into account as we send and receive information about the universe around us and about our world and the worlds we’re trying to communicate with.
In trying to define time, poor Aspie and Patla in their paper from NIST, they set out to look at not just how time passes on the moon, but they also considered the various Earth-moon Lagrange points as places we also need to take into consideration because this is where we’re looking to put things like the Lunar Gateway. This is where we’re looking to put communication satellites to communicate with the far side of the moon. All of these different places have different passages of time.
[Fraser Cain]
And it’s interesting, if you go back to that definition that you provided, it’s that you were assuming a soliton that is in orbit around the moon or a soliton. And that’s interesting because that’s very similar to the way the astronomical unit is described. Like the astronomical unit, the rough version is it’s the average distance from the sun to the earth.
But in fact, that isn’t accurate because the earth is pulling on the sun and that’s causing a wobble on the sun’s position. And so actually the distance from the sun to the earth changes, not only because the earth is following an elliptical path around the sun, but also the fact that the earth, the sun is wobbling at tens of centimeters per second, forward and backward, thanks to the gravitational pull of the earth. It is, you know, they’re both orbiting around the barycenter.
[Dr. Pamela Gay]
And Jupiter, Jupiter’s the dominant factor.
[Fraser Cain]
Yeah, no, for sure, for sure. But, and so when you measure an astronomical unit, you are imagining a soliton. If you’re measuring, you know, according, if you’re going to follow NIST or whatever, it’s a soliton orbiting the sun because that has no mass.
And that is, that is theoretically not pulling back and forth. On the sun. And, and so the reality is, is inaccurate by a certain wide margin, not just because of the movement of the earth, but also the, the movement the earth causes to the sun.
And so when you’re considering this, you know, they very specifically said, we’re going to consider a soliton because if we consider something that has mass, then that is going to affect the, the, you know, the positions of things and just make things even more complicated. And so, um, it’s, you know, a lot of the times we have these conversations on astronomy cast about things that are theoretically possible, but practically not relevant. Like, could we look backwards in time by looking at the light that was going around a black hole to see a time in the past?
Yeah. Theoretically photons are making the journey from the earth out to a black hole. They’re coming around the backside of the black hole and they’re making their way back to us theoretically, but practically no.
But in this case, time slices of time that are so small, um, are actually practical. Yeah. Having a practical implication to the way we will conduct our exploration to the point that like people could die if you get this time wrong.
[Dr. Pamela Gay]
Yeah.
[Fraser Cain]
And so we have to take into account, and yet it is mind bendingly complicated. Like, I don’t think anybody will ever go, Oh yeah, we lost 60 microseconds today. Like you do.
[Dr. Pamela Gay]
Well, and then you have to like consider the fact that we have stuff like leap seconds here on the surface of the earth.
[Fraser Cain]
Yeah.
[Dr. Pamela Gay]
And so when earth leap seconds, what do you do with the rest of the solar systems time? Because that leap second is aligning us with our world’s orbit and rotation relative to the sun and stars. Other worlds aren’t going to have those exact same needs for realignment.
And there’s stupid stuff that changes on the surface of our planet. Like when China put together their, what is it? Five gorges dam?
[Fraser Cain]
Three, three gorges dam.
[Dr. Pamela Gay]
Three gorges dam. Uh, that changed the rotation rate of our planet because the moment of inertia changed and we have to periodically upgrade.
[Fraser Cain]
The rotation of the earth is slowing down because the moon is moving away from us. And, and so, and I forget the exact number. I’m like, I’ve just noticed this and I’m sort of incorporating it, but it’s like on the order of tens of micro seconds per day per century is being caused by, by this slow, you know, the earth’s rate of turning is slowing down in a, in a rate that is measurable.
And I think you’re exactly right. You know, when you, when we deal with leap seconds or it’s this, you know, it was, it was fine and now it’s, now it’s not fine. Now we have to go back a whole second.
Does everybody across the solar system or do we switch to, there is no such thing as leap seconds. There’s no such thing as years anymore. You just accurately measure.
Yeah. Star dates. Yeah, exactly.
Is this star dates?
[Dr. Pamela Gay]
I think, I think it starts to become that.
[Fraser Cain]
Yeah.
[Dr. Pamela Gay]
We have Julian dates that we use in astronomy that go back to a set time and get calculated forward and it gets messy.
[Fraser Cain]
Um, so yeah, I mean, so what is the, I don’t know the, the way it works in Star Trek when, where does the star date originate?
[Dr. Pamela Gay]
I don’t, I don’t know. And, and I wonder, do you know this? I, I’m realizing.
So with earth, we have one moon that creates enough havoc for us and because it is moving away from us because it’s orbital rate around the earth is longer than the length of our day, it moves out. Now, Mars has two moons, one that has an orbital period shorter than its day and one that has an orbital period longer than its day, which one dominates. What’s its rotation doing?
[Fraser Cain]
I think it’s, I think Phobos is dominating. So it’s speeding up its rotation until Phobos is destroyed. Okay.
And then it’ll be Deimos that dominates and slows it back down again.
[Dr. Pamela Gay]
Yeah. So not our problem, at least.
[Fraser Cain]
No, no future Mars problem.
[Dr. Pamela Gay]
Yeah.
[Fraser Cain]
But yeah, yeah. It, it still just kind of blows my mind that, that our technology is so accurate. We deal with these wavelengths that are nanometers across.
Our technology is, is depending on this kind of stuff and we’re getting to this place in our, in our sort of world, our advancement, that these are issues that we have to take into consideration or things break, right? Ships go off course if you don’t take into account relativistic issues, you don’t take it, just time dilation into account for the GPS satellite systems. And now ships will go off or off track when they’re trying to go to the moon because we’re not getting the time right or we will.
Yeah. Yeah. And so you’re going to have a clock on board that is adjusting based on that.
And then you think about, say, um, uh, like the, the, you know, I am Legion, we are, we are Legion, I am Bob series where he has communications between different versions of Bob and they are moving at different rates of relative to the speed of light and they have to experience different amounts of time dilation as they try to talk to each other. And then they have ways of accounting for that, where, where one version will just wait around or do other things, waiting for the frames to come in for another version of himself. And, uh, you know, I guess it’s like, you know, nice problems to have that we’re so advanced that we now have to take into account relativistic effects when we attempt to communicate.
I think it’s great.
[Dr. Pamela Gay]
And this is where ultimately pulsars will form one of our most important coordinate systems. Uh, we’re going to rely on how time passes relative to those objects. And this is one of those things that the foundation series, which I need to go back and rewatch because I haven’t watched the second season yet.
Um, the foundation series really hits on this, looking at how time passes as you travel and how you measure your place.
[Fraser Cain]
Well, I think we should cover the, for Pulsar Timing as a feature episode and talk both about that, the Pulsar Timing Network as a, you know, as a gravitational, we talked about gravitational waves, but also as a potential way of timing, some interesting work on that. So that’s a future show.
[Dr. Pamela Gay]
Could be next week.
[Fraser Cain]
Maybe, sure. Thanks Pamela.
[Dr. Pamela Gay]
Thank you, Fraser. And thank you so much to our patrons who allow us to have a team that usually cleans up what we can do. Although I don’t think Rich is going to be able to correct what my hair did to this episode’s audio.
I am so sorry, everyone. Uh, this week in particular, we would like to thank Ellen Gross, Alex Cohen, Andrew Stevenson, Bebop Apocalypse, Brett Moorman, uh, Cammy Rassian, Daniel Loosley, Danny McGlitchie, David Gates, Disastrina, Dr. Woe, Dr. Jeff Collins, Ed, Elliott Walker, Father Prax, Frank Stewart, G. Caleb Sexton, Gerard Schweitzer, Gordon Dewis, uh, Gregory Singleton, Jarvis Earl, Jeff Huna Mortar, uh, Jeff Wilson, John Drake, Keith Murray, Kellyanne and David Parker, Kimberly Reich, uh, Christian Golding, Laura Kettleson, Lee Harbourn, Mark Phillips, Matthew Horstman, Matthias Hayden, Michael Perchata, Mike Dog, Nyla, Noah Albertson, Red Bar is watching, Share some Simeon Torfason, Ziggy Keemler, Stephen Veit, The big squish squash, The lonely sad person, Travis Sea Porco, Adam Anise Brown, Adam Moore, Arctic fox, Benjamin Mueller, Bob Zetski, Buz Parsec. I went into next week’s names. Some of you will get thanked twice. Thank you all so much for joining us and making what we do possible.
[Fraser Cain]
Thanks everyone and we will see you next week. Goodbye.
[Dr. Pamela Gay]
Astronomy Cast is a joint product of Universe Today and the Planetary Science Institute. Astronomy Cast is released under a Creative Commons attribution license. So love it, share it and remix it.
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