Complex Numbers

Time Out

Back before the welcome Birthday Week diversion, I featured an article from Ars Technica on how they're coordinating time between Earth and Moon: "Moon Time" 

Then, I wrote: "I have a couple of articles about this, from different perspectives." Well, today, the other article popped up. Being from Atlas Obscura, this one may be a little more approachable, but it also gives me more opportunity to be pedantic.

    Moon Time Is a Thing Now—Here’s Why It Matters  
Physicists recently created Coordinated Lunar Time, a time zone for our Moon.

On the Moon, there is no normal. There is no wind, no rain, no erosion.

Leaving aside that these things are "normal" for the moon, there is some wind (the solar wind) and some erosion, though that process works a good bit more slowly there.

Nothing flies overhead, and nothing green strains toward the sky.

...yet.

There are no daily rhythms like those we experience on Earth—no chirping of crickets, no sunset breeze.

I could live with the former, very easily. But there's also no air, so I wouldn't live very long.

A lunar day and a lunar night each last two Earth weeks.

Roughly. This corresponds with the phases of the moon, and is the result of the Moon always showing the same hemisphere to Earth, and its orbit around our planet. It's all very Newtonian.

What’s more, seconds tick by slightly faster than they do on our home world.

That effect is relativistic.

To understand why Moon time is so strange—and why scientists recently created a new and unique time zone just for the Moon—we have to spend a moment with Einstein.

People think of Einstein, they think of the famous equation. But time dilation is another thing entirely. He figured out a bunch of different shit; that's why they called him a genius.

Special relativity explains how different places in the universe perceive time and space differently; time seems to move more slowly in a larger gravitational field, relative to a lower gravity environment. And a clock moving through space ticks more slowly than a stationary one.

I have no quibbles here. It's just really hard to grok, because it's outside our everyday experience.

In the Hollywood interpretation of these theories, a character traveling in space for a long time, or under the gravitational influence of a black hole or other very large object, will age much more slowly than his loved ones on Earth.

As usual, Hollywood tends to exaggerate for the spectacle. You have to be traveling pretty damn close to light speed to experience that effect without precise measuring tools. And by "large," the author here means "massive." Black holes are generally pretty small, on a cosmic scale.

GPS satellites have to account for it in order to work. So every time you get directions on your smartphone, you experience the practical effects of special relativity.

I've noted this before, but it's relevant here.

In fact, all navigation is really about time. We invented longitude for this reason.

And I've talked about this, as well. Latitude is pretty easy to figure out. Longitude is a lot trickier.

First, we needed to invent a prime meridian, an imaginary line drawn from pole to pole along the planet’s surface. Then, for navigation, you need to figure out where you are relative to that fixed line. The simplest way to do this is to use a time scale that is the same at both locations. So longitude is really about clocks.

There's been a lot of talk lately, among some science video channels I occasionally watch, about how the Greenwich Meridian, the 0 degree longitude line, is in the "wrong" place. But ultimately, it doesn't matter where we put it, as long as everyone agrees on it. An earlier Prime Merdian went through Paris instead of a suburb of London, and I'm sure the French are just pleased as punch that everyone went with the English definition. So pleased that, even though France is mostly south of England, they use the next time zone to the east.

The only relevant thing here is that one needs to define a Prime Meridian for the Moon, which I'm pretty sure they've already done.   I say it should have gone through the center of Armstrong's first footprint, but no one listens to me.

Anyway, the article goes into how GPS accounts for relative time for Earth.

But we can’t just port this system over to the Moon. Clocks on the lunar surface actually tick faster than Earth clocks by almost 58 microseconds per day. It’s not much in a given day, but over the months it will add up, and it’s enough to disrupt the precise timing of GPS.

And thus, the calculation of latitude/longitude.

“It’s like having the entire Moon synchronized to one ‘time zone’ adjusted for the Moon’s gravity, rather than having clocks gradually drift out of sync with Earth’s time,” NIST physicist Bijunath Patla said in a statement earlier this month.

As good a summary as I've seen.

The physicists say their efforts to develop Coordinated Lunar Time could be applied to other places in the solar system, simply by adapting the clock system for any other world’s gravity.

Yeah, not really "any." The world would need to have a definable surface, which some of the larger planets don't. But we're not about to live in Jupiter's atmosphere anytime soon, so, fine.

It’s about time.

Thanks, now I can't use that pun in this entry's title.