Researchers Figure Out How To Keep Clocks On the Earth, Moon In Sync 66
Ars Technica's John Timmer reports: [T]he International Astronomical Union has a resolution that calls for a "Lunar Celestial Reference System" and "Lunar Coordinate Time" to handle things there. On Monday, two researchers at the National institute of Standards and Technology, Neil Ashby and Bijunath Patla, did the math to show how this might work. [...] Ashby and Patla worked on developing a system where anything can be calculated in reference to the center of mass of the Earth/Moon system. Or, as they put it in the paper, their mathematical system "enables us to compare clock rates on the Moon and cislunar Lagrange points with respect to clocks on Earth by using a metric appropriate for a locally freely falling frame such as the center of mass of the Earth-Moon system in the Sun's gravitational field." 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.
Things get complicated because there are so many factors to consider. There are tidal effects from the Sun and other planets. Anything on the surface of the Earth or Moon is moving due to rotation; other objects are moving while in orbit. The gravitational influence on time will depend on where an object is located. So, there's a lot to keep track of. Ashby and Patla don't have to take everything into account in all circumstances. Some of these factors are so small they'll only be detectable with an extremely high-precision clock. Others tend to cancel each other out. 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. 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. Which, given the pace at which we've sent things beyond low-Earth orbit, is probably a healthy amount of future-proofing. The findings have been published in the Astronomical Journal. A National Institute of Standards and Technology (NIST) press release announcing the work can be found here.
Things get complicated because there are so many factors to consider. There are tidal effects from the Sun and other planets. Anything on the surface of the Earth or Moon is moving due to rotation; other objects are moving while in orbit. The gravitational influence on time will depend on where an object is located. So, there's a lot to keep track of. Ashby and Patla don't have to take everything into account in all circumstances. Some of these factors are so small they'll only be detectable with an extremely high-precision clock. Others tend to cancel each other out. 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. 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. Which, given the pace at which we've sent things beyond low-Earth orbit, is probably a healthy amount of future-proofing. The findings have been published in the Astronomical Journal. A National Institute of Standards and Technology (NIST) press release announcing the work can be found here.
Not to mention (Score:5, Funny)
Daylight Saving Time ?
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Daylight Saving Time ?
Those living perpetually on Zulu time or within STRATUM-1 accuracy, don’t really have time for such silliness.
Lets hope those we export to another planet are smart enough to keep track of what the Earthlings pointlessly fret over.
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What I don't get about DST is why we only change it twice a year and not every season. Just having spring and autumn but ignoring summer and winter seems like a huge oversight.
Re:Not to mention (Score:4, Funny)
To be fair, astronaut Neil Armstrong seemed to anticipate the dilemma over leap seconds with his quip about small steps equating to giant leaps due to the differences in gravity. :)
Re:Not to mention (Score:4, Funny)
Daylight Saving Time ?
Already accounted for. The luna day is 24h and 50 minutes long, so you get that extra hour of daylight every day of the year. :-)
There will be riot police (Score:2)
When the bars will still close at the usual time (it will still feel one hour too early)
Re: Not to mention (Score:2)
No, you get one day per year. Think about it.
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Re: Not to mention (Score:2)
The earth revolves around the sun, one cycle is called a year. The moon revolves around the earth, during that time it also rotates on its own axis once.
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Precisely (well almost). It's all relative to something else considered fixed. Seen independently, the earth rotates on its own axis 366.24 (rounded) times per cycle of its sinusoidal path. Or the earth is stationary, both translationally and rotationally, and we're back to where we were centuries ago. Of course all of these views are indepedently valid.
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That's about the time it takes the moon to return to the same azimuth from a position on earth (a tidal lunar day). The time it takes a point on the moon to go through a complete sunlit/darkness cycle (e.g. from full moon to full moon) is around 29.5 days.
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The time it takes a point on the moon to go through a complete sunlit/darkness cycle (e.g. from full moon to full moon) is around 29.5 days.
I suggest we implement a Daylight Wasting Time then.
Re:Galactic Time Coordinates (Score:4, Insightful)
Confused as to what the U in UTC refers to? Can't be very universal then. :)
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While you may take it as why the global convention changed from calling GMT+/-X to UTC+/-X, they are technically different. "Greenwich Mean Time" was derived before the invention of atomic clock, from astronomical observation in Greenwich Observatory. Thus there were no such thing as "leap seconds". If the Earth slows down in rotation, you slow down the definition of second too.
Now, GMT is taken as a timezone of UTC+0. "Universal Time Coordinated" is defined by atomic clocks on Earth + leap second insert
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"... the origin was chosen at Greenwich observatory but, for the 1936 re-triangulation ... "
"The Mercator projections", Osborne, P (2008).
Good to know. :)
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GMT and UTC can be different by up to about 2 seconds depending on how fast the earth is spinning. GMT doesn't have leap seconds, UTC does, to bring it back more closely in alignment with GMT.
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It's actually (mostly) a French thing. That way they no longer have the name of a British place (Greenwich) in the name.
I assure you, the Irish get quite testy about this also. I once referred to "GMT" in a call with a customer in Ireland and thought I'd lost the customer. Lesson learned :)
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I stayed at a bed and breakfast in Ireland once. The lady who owned and ran it was chatting with us if we were American. No, Canadian. Oh, that's pretty much the same thing isn't it? Sure, I said, just like you're pretty much English.
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It's actually (mostly) a French thing. That way they no longer have the name of a British place (Greenwich) in the name.
I assure you, the Irish get quite testy about this also. I once referred to "GMT" in a call with a customer in Ireland and thought I'd lost the customer. Lesson learned :)
Just tell him you meant Guinness Mean Time ... :-)
[ Although that's apparently now owned by a British company, which might annoy him more. ]
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Yes, Dublin Standard time is 1 hour ahead of UTC, and they turn their clocks back 1 hour in the winter. So their timezone is legally different to the UK, but the same in practice.
Re:Galactic Time Coordinates (Score:5, Informative)
Well, UTC was created nearly a century ago. Things like "relativity" were fairly new concepts and definitely just ideas - things like spacetime, gravity wells, clock synchronization was limited to what was known. The fanciest form of time manipulation involved flight which was still a relatively new concept.
However, the problem is NOT new - it's the whole reason Star Trek never really dealt with dates per se - we have things like years and such, but they aren't used much because they rely on an Earth reference frame.
The whole concept of "Star date" is basically to serve as a universe-wide time standard - star dates take into account things like gravity wells, relativity, FTL travel, etc, such that you could do all sorts of fancy warping and orbiting and such and still have an accurate time. If someone books a meeting you all will show up regardless of how time actually flows.
That's why the normal "date" we use basically doesn't exist - the concept of days or weeks or months no longer really apply to a spacefaring culture.
Normally, we just kicked the can down the road - Apollo had used a concept called "mission clock" which is a clock that counted up in seconds from launch. This works fine as long as your missions aren't very long. The ISS remains in Earth orbit, so they use UTC time even though it doesn't make much sense. Antarctica uses New Zealand time as that's their last port of call.
But once you start getting into things like relativity and such, suddenly keeping time becomes important.
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Well, UTC was created nearly a century ago. Things like "relativity" were fairly new concepts and definitely just ideas - things like spacetime, gravity wells, clock synchronization was limited to what was known. The fanciest form of time manipulation involved flight which was still a relatively new concept.
When International Astronomical Union introduced the term "Universal Time" in 1928, Einstein's Relativity, both Special and General, have already been published. When "UTC" become an official term in 1967, nobody in Science were unheard of Einstein's Relativity.
Therefore in theory they could have named UTC as TCT instead, for "Coordinated Terrestrial Time" or "Temps Terrestre Coordonne".
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UTC is indirectly based on Terrestrial Time via TAI. The U doesn't mean this is the actual time everywhere, it means this is the time we're going to use everywhere. I'm sure it will remain so: even people on the moon aren't going to set their watches to baycentric time or whatever, they'll use UTC (+ 0 or whatever it is in their capital or where they launched from).
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Eventually, if humanity become multi-stellar without mastering faster-than-light communications, it will be impossible to communicate leap second updates across solar systems before they are to be in effect. So the current form of UTC will become unsustainable in its current form.
Solution 1: Give up leap seconds and let clock time on Earth mismatch mean solar time gradually.
Solution 2: Perform some form of geoengineering, such that the Earth rotate in the "correct" speed and no leap seconds are needed f
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There's very little point in trying to communicate a time of day standard across a significant distance, never mind interstellar.
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We should all be using Galactic Time Coordinates which are derived from the quantum gravitic oscillations of SagA* at the centre of our galaxy.
I think you need to solve the 3 body problem first before you solve the 100 billion body problem.
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Galactic Time Coordinates - Pedantic (Score:2)
PTP server? (Score:2)
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Simply because time passes differently in different gravitational potentials, and there is no absolute, universal time that we can all synchronize to; if that would be possible to exist (i.e., the absolute universal time), it would contradict both special and general relativity.
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You might as well pick the earthbound one since everyone else is using it.
Well, we are talking about coordinating time on the moon as well as on this planet... so the logical frame of reference would be the local star, aka the Sun. Since we are also looking to go beyond the influence of our star, using the black hole at the center of our galaxy makes the most sense as far as future expandability goes.
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Ideally, a time reference at the event horizon of the black hole?
I was thinking more along the lines of using red shift. Time stops at the edge of a black hole. This is the one true 'zero' we get in the Universe. So start measuring at some point where the redshift of the light starts becoming less smeared. Something that is measurable and testable between observers.
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We could and we will. That's what we do with TAI and UTC now. They're averages that ignore little details like what elevation you're at and whether you're sitting on a bunch of iron deposits or sand.
We still use local clocks to measure how fast things happen, because that depends on the local time, not the agreed upon convention.
TL;DR version (Score:2)
Scientists: "Synchronize on my mark.... mark!" /s
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"That didn't work. Somehow our clocks ended up 1.28 seconds apart again."
"Oh, yeah. Well, let's keep trying until we get it right. Ready...? Mark!"
Not universally solvable. (Score:2)
There's basically no straightforward solution without specifying punctual conditions as the spacetime reference frames differ in so many ways. General relativity is a bitch.
Why? (Score:2)
Serious question. Any scientific experiment requiring high precision timing will either be local enough that synchronizing with Earth won't matter (or be unique enough it'll be custom-calculated). Any remote instrument operation with timing precision finer than the speed of light delay is pointless.
What's the practical application of this?
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That's not clearly true. Sometimes you might want a really large separation. (OTOH, it would be hard to predict the exact length of that baseline.)
Possibilities (Score:2)
My immediate guess would be the equivalent of a space-GPS, where you use beacons from satellites, and a couple on the moon to precisely triangulate your position when you are in between the earth and the moon.
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I know it's crazy, but it's true
If you get caught between the moon and New York City
The best that you can do
The best that you can do is fall in love
Arthur (Score:2)
Isn't that song about a drunkard? I guess he'd need a GPS going to the moon.
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From A Deepness in the Sky by Vernor Vinge. (Score:4, Interesting)
Pham Nuwen spent years learning to program/explore. Programming went back to the beginning of time. It was a little like the midden out back of his father’s castle. Where the creek had worn that away, ten meters down, there were the crumpled hulks of machines—flying machines, the peasants said—from the great days of Canberra’s original colonial era. But the castle midden was clean and fresh compared to what lay within the Reprise’s local net. There were programs here that had been written five thousand years ago, before Humankind ever left Earth. The wonder of it—the horror of it, Sura said—was that unlike the useless wrecks of Canberra’s past, these programs still worked! And via a million million circuitous threads of inheritance, many of the oldest programs still ran in the bowels of the Qeng Ho system. Take the Traders’ method of timekeeping. The frame corrections were incredibly complex—and down at the very bottom of it was a little program that ran a counter. Second by second, the Qeng Ho counted from the instant that a human had first set foot on Old Earth’s moon. But if you looked at it still more closely... the starting instant was actually about fifteen million seconds later, the 0-second of one of Humankind’s first computer operating systems.
this is a wast of time (Score:2)
Back in the day (Score:2)
Back when land lines were still a thing I could call a local number and get, "At the tone, the time will be xx:xx and the temperature is xx". While the temperature may be irrelevant for Moon purposes the time could be useful. Surely a simple phone call once day to NASA would do to update the time.
OR we continuosly transmit a time signal (Score:2)
Pulsar timing seems more reliable.. (Score:2)
Hmm, I'm sure these fine scientists have spent a hell of a lot more time thinking about this topic than me, but I have to wonder about how good is something that depends on the center of mass of the Earth-Luna system.
I mean, if you launch a rocket to Mars or a probe to Pluto, Earth's mass will be reduced so the center of mass would change. Micrometeor and comet dust capture? Whatevah.
Broadcasting a time as somebody mentioned is one way, though estimating latency is problematic. How about a time system that
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You may very well be right. I started reading their paper [iop.org] and it is fascinating. So far it seems aimed at comparing and estimating clocks in the Earth-Luna system on the order of nanoseconds. So pretty accurate, but not as accurate as some experiments.
If something big entered this system like a mile-wide asteroid that would likely perturb things but I have not gotten into the math. The main takeaway I got is the difference of gravitational potential is what makes clocks run faster - perhaps 58 microseconds
Time is an illusion... (Score:1)
Is my math correct? (Score:2)
TFA says "an object near the surface of the Moon will pick up an extra 56 microseconds every day".
So, since a year is 365.242374 days long, an object near the surface of the moon will pick up 20.453573 Milliseconds each year. That's about 5 Milliseconds longer than my ping times to Google DNS right now.
If we consider that modern Homo Sapiens have been around for about 100,000 years, the moon has picked up 34 seconds since modern man walked the Earth.
Since the end of the age of dinosaurs (65 million year ag