Complex Numbers

Moon Time

I have a couple of articles about this, from different perspectives. This one, from Ars Technica, gets a little, well... technical.

    Researchers figure out how to keep clocks on the Earth, Moon in sync  
A single standardized Earth/Moon time would aid communications, enable lunar GPS.

I'm pretty sure I've talked about this sort of thing in here before, but if so, that was before they'd figured this out. I found one example: "Luna Ticks" 

Our communications and GPS networks all depend on keeping careful track of the precise timing of signals—including accounting for the effects of relativity.

From what I understand, there are two opposite effects of relativity with GPS. One is the relative speed of the satellites; the other is their elevation. While opposite, they inconveniently don't cancel each other out.

You also have to account for distance from receiver to each satellite, because of the speed of light. I mention this because while the lag time to satellites in low earth orbit is small, the moon is about 1.3 light-seconds away, and a second and a third (pun intended, of course) is a long damn time for some things.

It's relatively easy to account for that on the Earth, where we're dealing with a single set of adjustments that can be programmed into electronics that need to keep track of these things. But plans are in place to send a large array of hardware to the Moon, which has a considerably lower gravitational field (faster clocks!), which means that objects can stay in orbit despite moving more slowly (also faster clocks!).

No mention here of accounting for the variable gravitational field of the Moon, which I've seen described as "lumpy." I trust they've figured out how to deal with that, but if not, I'm certain we'll hear about it in an "oopsie!" article in the future.

It would be easy to set up an equivalent system to track time on the Moon...

I think this author has a different definition of "easy" than I do.

I might have chosen "straightforward," instead.

...but that would inevitably see the clocks run out of sync with those on Earth—a serious problem for things like scientific observations.

Relativity put a dagger in the back of the concept of "simultaneous;" two space-time events that seem to be simultaneous for one observer can be asynchronous for another. This is generally not an issue on Earth, and doesn't matter to our day-to-day lives (as long as we're not physicists), but I expect it makes a difference when dealing with separate worlds.

So, the International Astronomical Union has a resolution that calls for a "Lunar Celestial Reference System" and "Lunar Coordinate Time" to handle things there.

Yawn. Come on, you can do better than that. "Loonie time" is right there on top of my brain. Give me a few minutes (and a few drinks), and I might even come up with some forced acronyms, like "Lunar Uncoupled Normative, Asynchronous, Temporal Isochronic ClockS."

And that's without benefit of beer.

Anyway,

We're getting ready to explore the Moon.

Son, we've been exploring the Moon since before I was born. Just not very often by way of humans visiting the place.

We'll have an increasing set of hardware, and eventually facilities on the lunar surface.

Or under it, as I noted in another entry: "Cave People" 

All that could potentially be handled by an independent lunar positioning system, if we're willing to accept it marching to its own temporal beat. But that will become a problem if we're ultimately going to do things like perform astronomy from the Moon, as the precise timing of events will be critical.

Thing about lunar astronomy is... well, it's obvious that not having an atmosphere helps a lot with observations, but we have space telescopes for shit like that. No, the thing is, to the best of my limited understanding, you can put a telescope on the Moon and one on Earth and one out in space, and what you get is effectively one big giant telescope, able to resolve distant objects to greater precision.

That is, if all your you get all your ticks and tocks lined up right.

As always, it's possible I got something wrong there, but the point is, I can see how synchronization would be important when doing astronomy between Earth and some other world.

What does this look like? Well, a lot of deriving equations. The paper's body has 55 of them, and there are another 67 in the appendices. So, a lot of the paper ends up looking like this.

If you want to get heart palpitations, go to the article to find out what "this" is.

Still, using their system, they're able to calculate that an object near the surface of the Moon will pick up an extra 56 microseconds every day, which is a problem in situations where we may be relying on measuring time with nanosecond precision.

This sort of thing is why I strongly object to airy "time is an illusion" proclamations. Nothing that can be calculated to that degree of accuracy deserves to be reduced to "illusion." It may not be fundamental, sure, and it's probably an emergent property, but so is temperature.

If time is an illusion, then it's time (pun intended) to revise the definition of "illusion."

And the researchers say that their approach, while focused on the Earth/Moon system, is still generalizable. Which means that it should be possible to modify it and create a frame of reference that would work on both Earth and anywhere else in the Solar System.

Mars or bust!