The headline here might really be the White House has actually ordered something that makes sense.
On Tuesday, April 2nd, the White House’s Office of Science and Technology Policy released a document that directs NASA to develop a strategy by the end of 2026 to create Coordinated Lunar Time (LTC), a new time standard based on Coordinated Universal Time (UTC) on Earth but adapted to operations on the moon.
“As NASA, private companies and space agencies around the world launch missions to the Moon, Mars and beyond, it’s important that we establish celestial time standards for safety and accuracy,” Steve Welby, OSTP deputy director for national security, said in a statement.
UTC is a very useful standard here on Earth, but relativistic effects start to show up in cislunar missions. One of the seemingly bizarre conclusions of special relativity is that clocks change the rate they run as the distance from the center of a gravitational field changes. Clocks on mountaintops run faster than clocks in valleys, and clocks in cislunar space will run faster than clocks on Earth. To an observer on the Moon, an Earth-based clock will appear to lose an average of 58.7 microseconds per Earth-day with additional periodic variations. If you're used to working in microseconds, that seems like a large number, but it would take around 50 years for it to approach a 1 second difference.
Standard time on Earth is inextricably linked to the day/night interval and the Earth's rotation in 24 hours (approximately, "with additional periodic variations"). The traditions of how the day was divided into hours, time zones and everything else don't seem transferable to the moon. If you pick one point near the lunar equator and define the time the sun rises as zero, the time of sunrise one lunar day later will be close to 28 complete Earth days. Instead of 24 hours, the lunar day is more like 28*24 or 672 Earth hours. The lunar day doesn't need to be exactly 672 hours, but crews working together need to be able to communicate and work with the required accuracy; whether Earth to moon or elsewhere.
“As NASA, private companies and space agencies around the world launch missions to the Moon, Mars and beyond, it’s important that we establish celestial time standards for safety and accuracy,” Steve Welby, OSTP deputy director for national security, said in a statement.
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“A consistent definition of time among operators in space is critical to successful space situational awareness capabilities, navigation and communications, all of which are foundational to enable interoperability across the U.S. government and with international partners,” Welby said.
The policy sets four major features for LTC: traceability to UTC, accuracy sufficient for precision navigation and science, resilience to loss of contact with Earth and scalability to environments beyond cislunar space. All of those could be achieved with a similar network of atomic clocks, and times could be based on the SI standard for a second, the unperturbed ground-state hyperfine transition frequency of the cesium 133 atom, to be 9,192,631,770 Hz or 9.192631770 GHz.
NASA has been working on a concept called LunaNet to provide communications and navigation services at the moon using an interoperable network that could include commercial and international contributions. NASA and the European Space Agency have produced several versions of a LunaNet Interoperability Specification that mentions the creation of a Lunar Time System Standard, although documentation for that has not been developed.
In May 2023, the National Geospatial-Intelligence Agency (NGA) announced it was working with NASA to develop a positioning and navigation system for the moon. The goal, NGA officials said then, was to create a system for users on the moon that works “as accurately and as safely as GPS does on Earth.” That announcement did not go into details about creating a lunar time standard.
Here's a thought. On the equinox we just went through here on Earth, the sun
moved from rise to set, roughly 180 degrees in 12 hours. That works out to 15
degrees per hour. Here's a map showing the time zones. Along the top of the
frame, the numbers in light blue are each 15 degrees in longitude - one hour in sun position. In the
continents, time zones get adjusted too much and look all wonky.
On the moon, what's the practical width for a time zone? Not an hour; the sun goes 180 degrees in 14 days or 336 hours. Much too narrow; an Earth hour is 0.536 degrees. What should time zones be like on the moon?
No need for a time zone on the Moon, since all time is relative to Earth Time. So, just use UTC or whatever base starting and stick with it. Doesn't matter if you're out past Pluto or surfing the corona of the Sun, a 'human day' is still 24 hours. And who cares if it's dark or light on Mars when the control is being run from Boca Chica or Houston or Huntsville or Cheyenne Mountain (I won't accept control from Beijing or Moskva or Mecca, I just won't.)
ReplyDeleteSeriously, the dufuses are overthinking the issue. One Time, One Race. All of it based off of Zulu Time/Greenwich Time. The ChiCom Taiconauts are gonna use Beijing Time anyways, Cosmonauts will use Moscow Time, Allahnauts will use Mecca and/or Medina Time (and probably kill others for not using said time) and we'll just use Zulu-based UTC set to either Eastern or Central time.
Geez, people.
24 hours a day, 60 minutes an hour, 60 seconds a minute. 31/30/29/28 Days a Month, 12 Months a year. Doesn't matter a damned bit at all.
If this was soooo important it would have become an issue as soon as Voyager got out there a bit, or the Juno missions, or any other probe. Earth People can adjust their planetary work hours to meet the mission needs, and non-Earth People (either close to Earth or way out there on a multi-year or multi-decade mission) can adjust their time to whatever Earth time they are based upon.
Simple. Have whomever isn't on Earth use a comp program to adjust their stupid time and forget special timey wimey stuffy wuffy.
Geez. What a bunch of boneheads. We know how gravity and lack thereof affect atomic clocks. So we know how to compensate for the gravitational effect. For us USAians, base it upon the atomic clock at Cheyenne Mountain or the Naval Observatory in DC, and run whatever programs (on three separate machines, of course) on the spacecraft/station/outpost/base/whatever and have the damned machines fix it.
One Race. One Time.
Boneheads...
Yes, I understand there are some real issues, but it's what we humans do. Adapt, improvise, overcome.
I think this story is just another nameless, faceless bureaucrat trying to make himself/herself/zirself feel important. We already have UTC, just set the clocks to that and be done with it. Even if you took a clock from earth to the moon and didn't bother adjusting for relativistic changes you'd probably get more error induced from flaws in the clock than relativity.
DeleteI was going to comment, "just WHY does the Moon need time zones??" when I read what Beans just wrote. And, I think my point is valid - we don't really need 'em. Pick a Moon Time, offset (if necessary) from UTC, call it a day. Go home. Your work here is done.
ReplyDeleteSo, that's TWO opinions for the negative, what say all y'all readers? Chime in, folks. Don't be shy.
"Moon time" will be established by whoever creates the first "permanent" moon base. Anyone want to bet that will be the Chicoms?
ReplyDeleteNope. The Indians.
DeleteAnd it'll be a 7 Eleven
Did *I* say that?!?!
Will there be Moonlight Savings Time?
ReplyDeleteRemember that politicians will decide Lunar Time so the chances of getting some system that works, and it based in common sense is pretty close to zero.
I'm going to weigh in with Beans and Igor.
Until the Moon colonies revolt, (Yep, The Moon is a Harsh Mistress) the Loonies are going to use SET (Standard Earth Time).
It's going to be much, much, easier to just use timekeeping devices based on the SET than it is to make timekeeping devices that use Lunar Units of Time.
Mark has a point that is both correct and worrisome.
Yeah man! Epic Heinlein story. There is just something unworkable about the systems of governments, seeming contrivances, like as if they invent specific styles, and when they poop out they throw a new style on us, certainly if they did not serve elitists we would not have them, they all bleed us good folks white, like they are intended to specifically pluck the golden goose feather at a time, and none last past a certain date, 75 years appears the max, then they change up, some other faction is given domination status. As you say, who comes up with this stuff anyways really? How its all out of wack, and natural unfettered looks better and better every day, and how that itself is constantly stomped on, like better not let the little guy get a taste of freedom, need another way to hide what is naturally best for us, leaving nothing to chance. I guess to control it all you got to control all of it. Thats the time system of absolute power. Day light savings, another control, its worthless for anything else. Maybe its about time in the sense controlling "time"... tick tock... as we are led to perceive it, by some basis of rules unseen, is really about a form of absolute power?
DeleteAnd speaking of TMIAHM, Heinlein addressed the question of moon time in that novel, specifically when Prof and Manny visited Earth. Heinlein explains (through Manny's dialogue) that lunars are far too long to be human-compatible days, so the Loonies just set their clocks to Greenwich time (predecessor of UTC) and used a 24-hour day. Simple. No government bureaucracy required. I get the relativistic offset issue, but as Manny O'Kelly Davis would no doubt remind us: "Just let smart computer solve problem, cobber. No huhu."
DeleteI always thought of "time" being same everywhere, I was unaware that clocks actually differed depending on where they are physically located on the earth. But then I thought that "time" measuring was a tool to allow things to happen or to be counted on a level playing field, as much for communication as anything else.
ReplyDeleteAs long as things are Earth based GMT will work as long as you have a means of everyone having the same interval that we call seconds.
As to who establishes official time on the moon... keep your eye on the Japanese, the Chinese hardware looks a lot like they bought it surplus from the US ... and with the way the world is going don't ignore Elon Musk either.
In the middle of commenting, I looked up atomic clocks because I remembered from Science! Class! in school that ACs were da bomb and always correct. Only to find out that they are not, in fact, always correct because gravity affects subatomic particles and atomic decay. Was very shocked. Thus, computer programs to compensate for gravity variables.
DeleteBeans and the others are driving the nail. Creating a special moon time is another tax payer swindle.
ReplyDeleteSiG, your time zone chart of the world doesn't have the alphabet time zone designators on it. War in Korea was on I time not Z.
Dave
Thousands of years we used the moon and sun cycles to keep time. Foundational in every sense, rhythm to it, orbital mechanics are as dependable system of time tracking as sub atomic rhythm keeping. What system of time tracking could be more common sense? After all its totally natural and dependable. Who makes up these strange weird unnatural decrees by what authority? So strange. More so every day now.
ReplyDeleteI just got this gut sense lately something about time has changed somehow, been trying to wrap my mind around it, another thing, how the suns light has a slight different hue to it, noticed our solar panels output increased too, not a whole lot, the batteries seem to charge a bit faster, especially noticeable over this past winter sun angle. Not a radio buff like a lot of you all on here so not keeping track of it. Has there been changes unusual in atmospheric radio wave propagation? Weather seems out of character in my part of the woods too this last year or so.
Hubris disguised as "time" control. What is more preposterous than decreeing daylights savings is something in the first place, like the great Indian axiom about the white man cutting off the bottom of his blanket, sewing it to the top, calling it longer.
ReplyDeleteNobody yet has explained exactly what time truly is.
A great wonder and a timeless mystery.
And that other old timey saying about what comes before which drives insanity?
White rabbits and pocket watches... "mumsey where the burrow groves.."
Time is a measurement of entropy. Period.
Deleteone of the greatest/most exciting/most educational things about reading Sig's column is the commentors.
ReplyDeleteAgreed!
DeleteA LOT of sharp Engineers and scallywags here, for sure!!
DeleteYar! Ye be not touching me Atomic Clock, ye blackguard! Yar!!!
DeleteI think a lot of commentators are missing the concept that elapsed time is *moving at different rates* based on your position in a particular gravity well.
ReplyDeleteThe most naïve implementation would be to start moon time on January 1, 2030 as being the same as Greenwich standard time.
But by the end of the day the moon would be 58.7 µs ahead of Greenwich time. By the end of the year this would've increased to 2/100s of a second, which is a huge amount in engineering and science applications.
A naive "fix" would be to add a negative leap period of 58.7 µs at the end of each lunar day, but then events at, say, 23:59 would be further fron sync with Earth than those at 01:01 hrs. Also, what to do about processes and events that cross the "midnight" boundary?
And that's not even adressing the fundamental issue that clocks are running at different relative speeds - about 60 microseconds a day, and computers are cycling in half nanoseconds.
And clocks on Mars, near Jupiter, near the sun, and far out past the heliopause will have similar problems. So whatever solution is adopted should be flexible enough to account for any clock in any gravity well.
An international convention to handle problems like this is a good thing to set up in advance.
I am guessing the Whitehouse OSTP order is probably a response to an internal request from NASA and the ESA (and maybe others) and is required to get the ball rolling.
Physics is physics. Clocks will run at different speeds in different gravity wells.
ReplyDeleteThe question is do we REALLY care that events seconds away via radio aren't synchronized to the nanosecond? As long as we know the offset things can be adjusted after the fact. X standard time is established by time standards located on X, any skew from Earth Standard Time (CUT) can be determined and calculated, after including the delays caused by changes in the Moon's orbit.
It is nonsense (to me at least) to talk about milliseconds of time slew when the round trip for a radio signal to other site is 2.4-2.7 seconds.
@Rick T: That's sort of what I said, an established and agreed upon protocol for adjustment.
ReplyDeleteI actually have a vague memory, of a presentation years ago, where it was mentioned in passing that the French time keeping organization sort of adressed this.
As to time at a location, I see a need for both Earth Standard Time and a solar clock that marks rotation and exposure to the sun. So Mars would be 'Mars Time,' a space station time would have 'orbit time' and so on.
ReplyDeleteJust use a Pulsar (or two) for the "tick". Everybody can see it, nobody can influence it.
ReplyDeleteWe have our ways of making it "tock".
That's just so simple that nobody would use it. But it does make sense. Just require everyone in space to set up a telescope pointing at said pulsar or pulsars and systems to count the tick.
DeleteJust about five years ago, I ran a piece that mentioned we have atomic clocks that are so precise and repeatable that differences in time due to gravity can be measured when they're separated vertically by one foot. That may be big gravity well on a white dwarf but doesn't seem like much here on Earth. It seems that the precision required for time depends on what it's being used for and anything they regulate will just be like a Time Zone. If it's midnight in UTC, what hour is it in what place on the moon? And that seems completely arbitrary. "It's five o'clock somewhere."
ReplyDeleteThe first settlement that has that first 7-11 may want to have their time the same as Bangalore or Beijing, and since the sun moves so slowly across their "sky," the rest could practically be at random.
Yes. Years ago I was helping set up a "swing test" to measure moments of inertia of a piece of aerospace gear (several tons assembled) and we had to know exactly what "g" was at the test site. It varies quite a bit over the Earth, and we were (then) shooting for 1% accuracy. After I left the project I understand they switched to a "spring test" with expected 15% error...
ReplyDeleteRandall Munroe on time:
ReplyDeletehttps://www.explainxkcd.com/wiki/index.php/2867:_DateTime