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Celestial Reference Frame Department

crf.usno.navy.mil

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Re: Celestial Reference Frame Department

#41

Post by fanf2 »

techdragon wrote: post #32
kortilla wrote: post #29

Earlier quoted context omitted.

The GPS-only clock source entered the room… I.e. most aircraft, spacecraft, electrical infrastructure, cell towers, etc. Welcome straight back to “what do we do with the leap second?” hell. Unfortunately none of the interfaces between parties agree on TAI. It’s stupid GPS time or UTC.

GPS never had leap seconds. Your hell is imaginary. It is a myth and a lie perpetrated by those that never looked beyond the convenient lie to children that is UTC and tried to understand the true nature of timekeeping. GPS Time signal = TAI minus 19 seconds https://aviation.stackexchange.com/a/90844

Actually it’s a bit more complicated than that. As well as the integer number of seconds between GPS time and UTC, the GPS signal includes a small linear correction (rate and phase) that gives you a more precise version of UTC(USNO). So to get something like TAI from GPS time you must also apply the rate and phase correction. But that still isn’t TAI as such, because TAI is only defined after the fact, in the form of retrospective corrections for each time lab’s implementation of UTC. So you would need to get Circular T from the BIPM and apply the USNO correction.

Re: Celestial Reference Frame Department

#42

Post by jdougan »

techdragon wrote: post #37
michaelmior wrote: post #35

Earlier quoted context omitted.

In English, I believe it's "International Atomic Time". Otherwise "Temps Atomique International" in French which is where the acronym comes from.

It is indeed “International Atomic Time” in English, for what it’s worth I chose to use the French version of the acronym because using the English text requires more explanation why the acronym for “International Atomic Time” is not IAT but TAI, than just using the French name which matches the acronym and letting the curious google some more about the topic. Also for bonus points the curious should read about UTC a…

It feels like something that would happen in Canada, an anglo/franco political compromise that is biased neither way and satisfies no one.

Re: Celestial Reference Frame Department

#43

Post by fanf2 »

Animats wrote: post #5
killjoywashere wrote: post #3

I did a deep dive on this once: Coordinated Universal Time (UTC) is coordinated among ... who? The answer (at least when I looked into it): University of Paris, NIST, and the US Naval Observatory. The other two are constantly comparing state of the art atomic clocks. USNO is the only member looking outward.

Those are the time people. There's also the Earth Rotation Service.[1] They track what the planet is doing. The Earth Orientation Center, in Frankfurt, Germany, tracks where the poles are pointed and the rotation speed. These are the people behind leap seconds. It all comes down to 3 numbers.[2] [1] https://www.iers.org/ [2] https://www.iers.org/IERS/EN/DataProducts/tools/eop_of_today...

The IERS web site says the EOC is at the Paris Observatory, but much of the data (such as Bulletin A) comes from the Rapid Service/Prediction Centre at the USNO.

Re: Celestial Reference Frame Department

#44

Post by jdougan »

techdragon wrote: post #34
t8sr wrote: post #30

Earlier quoted context omitted.

Huh? Ok, so what do you propose: should time keeping diverge from the day-night cycle, or should we have leap seconds? There is no third option - the Earth just doesn’t turn the way you want it to. It becomes your problem in a hurry once you encounter a 61-second minute and your stuff all breaks.

Not really disagreeing just expanding on the conversation… I’m pretty happy with computers storing time as a “weird number that we add another number to to get the human time”… because we are already usually storing it as second/millisecond/etc offset from an arbitrary fixed point in history… we’re talking about going from “current integer (prefix)seconds value -> (some math involving leap year formulas and fiddly st…

The general rule of thumb for helping people do periodic jobs reliably is to have the job be frequent enough you can't forget, on never have to do it. Too infrequent, and you forget what to do. Too frequent, and you get sloppy. I think the application to the leap seconds/minutes/hours situation is obvious.

Re: Celestial Reference Frame Department

#45

Post by fanf2 »

techdragon wrote: post #37
michaelmior wrote: post #35

Earlier quoted context omitted.

In English, I believe it's "International Atomic Time". Otherwise "Temps Atomique International" in French which is where the acronym comes from.

It is indeed “International Atomic Time” in English, for what it’s worth I chose to use the French version of the acronym because using the English text requires more explanation why the acronym for “International Atomic Time” is not IAT but TAI, than just using the French name which matches the acronym and letting the curious google some more about the topic. Also for bonus points the curious should read about UTC a…

UTC isn’t a mystery. There are various kinds of UT, depending on what corrections are applied to the raw observations: UT0, UT1, UT2. UT1 is the standard version of mean solar time, though GMT (when it was still a thing) used to be more like UT2. UTC is named according to the same scheme: Universal Time with a suffix denoting which kind of UT.

Re: Celestial Reference Frame Department

#47

Post by keepamovin »

h2odragon wrote: post #25
keepamovin wrote: post #16

Earlier quoted context omitted.

God doesn't roll blockchain...

Are we sure? Think that may be why "time" is such an intransigent thing to work with.

Not sure, I think hash functions could be deeply connected with the Inner Workings. Maybe time is a merkle tree...just kidding, but who knows?

It's all a big mystery. He could roll blockchain. But who knows? I just think there'd be a more elegant concept :) haha

Re: Celestial Reference Frame Department

#48

Post by throw0101b »

Animats wrote: post #5
killjoywashere wrote: post #3

I did a deep dive on this once: Coordinated Universal Time (UTC) is coordinated among ... who? The answer (at least when I looked into it): University of Paris, NIST, and the US Naval Observatory. The other two are constantly comparing state of the art atomic clocks. USNO is the only member looking outward.

Those are the time people. There's also the Earth Rotation Service.[1] They track what the planet is doing. The Earth Orientation Center, in Frankfurt, Germany, tracks where the poles are pointed and the rotation speed. These are the people behind leap seconds. It all comes down to 3 numbers.[2] [1] https://www.iers.org/ [2] https://www.iers.org/IERS/EN/DataProducts/tools/eop_of_today...

Someone submitted a 'story' for the IERS that's getting some votes:

* https://news.ycombinator.com/item?id=37777116

Re: Celestial Reference Frame Department

#49

Post by oh_sigh »

Avshalom wrote: post #28
jdougan wrote: post #18

Earlier quoted context omitted.

The International Earth Rotation Service is possibly my favorite name for an international bureaucracy. It give me visions of a Giant Control Lever extending deep into the Earth, with the labels Faster and Slower .

You can actually slow down or speed up the planet's rotation with a big switch. |_ open switch, slower __ closed switch faster You can also do it yourself by standing up or laying down

I wonder how big the switch would need to be to be able to transmit info via the rotational speed as hest we can measure it.

Re: Celestial Reference Frame Department

#50

Post by 9192631770_Hz »

twic wrote: post #22
mikeytown2 wrote: post #2

More information about the software they use https://en.wikipedia.org/wiki/Naval_Observatory_Vector_Astro... Manual: https://aa.usno.navy.mil/downloads/novas/NOVAS_F3.1_Guide.pd...

> Currently, NOVAS has three different editions, for C, Fortran, and Python. I imagine the Python versions wraps one of the other two. But are the C and Fortran versions separate, or does one wrap the other? If not, how are they related? Parallel implementations kept in sync by hand? Used to check each other? Machine translated? Code-generated from an upstream definition?

My knowledge is a few years out of date (but I would be surprised if the situation is different now). The Fortran is the primary version, the C is a parallel implementation that follows the Fortran, and the Python wraps the C. Calculations from each are compared to each other as well as calculations produced by https://iausofa.org/
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