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Celestial Reference Frame Department

crf.usno.navy.mil

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Re: Celestial Reference Frame Department

#31

Post by otteromkram »

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?

Numpy uses FORTRAN, so it might be a good place to start.

https://numpy.org/doc/stable/f2py/python-usage.html

Re: Celestial Reference Frame Department

#32

Post by techdragon »

kortilla wrote: post #29
techdragon wrote: post #19

Earlier quoted context omitted.

You have been lied to… your true enemies are the ones that continue to build monotonic systems on top of non monotonic time scales… Join us in the Temps Atomic International! TAI is the one true timescale. Computers should be using TAI and converting to UTC when humans want to see a local human time. My sincere belief is this was a bigger mistake than null, bigger than all the Y2K “we stored the year as 2 digits” stu…

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

Re: Celestial Reference Frame Department

#33

Post by hollander »

jdougan wrote: post #18
Animats wrote: post #5

Earlier quoted context omitted.

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 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 .

Think of what you can do as International Earth Rotation Manager! Probably not much, but what a job title!

Re: Celestial Reference Frame Department

#34

Post by techdragon »

t8sr wrote: post #30
RetroTechie wrote: post #26

Earlier quoted context omitted.

> (..) but just infrequent enough almost everyone can ignore it ... If it's only a problem for the experts, then it isn't really a problem, right? The experts can decide for themselves how hard they work on solving self-invented problems.

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 stuff not just x/365/24/etc) -> human display value” adding one single subtraction step to the some math part that that already has a bunch of other fast assembly arithmetic calculations involved in it.

As for divergence. We have two kinds of timekeeping. “Calendrical timekeeping” which will always get fixed to be close enough to the solar year that no one has a problem with it, and “Chronological timekeeping” which is basically the science of keeping a track of how many seconds have passed between arbitrary moments in time. All Calendrical timekeeping have for decades now been built on top of TAI and the science of Chronological timekeeping where metrologists have kept fastidious watch over atomic clocks and matched the beating of their resonating frequencies to the astronomical record keeping to allow ever more precise astronomy and the byproduct of this effort have been precise records of how long in scientifically precise seconds each day has been, and from these records we know we have to occasionally “add” a second if we want the “human time” to stay within 1 second of the astronomical time. Consequently we can simply decide we are happy with more or less drift. One second is small enough we can kinda just deal with it, but imagine having a leap minute every hundred years? Coordinate that mess, or how about a leap hour once a millennium? It’s trivial for people we don’t really time anything as humans faster than a second, so if we skip one it’s pretty much ok… it’s categorically on an issue for computers… which should never have used UTC and should have always used TAI because TAI doesn’t skip a second and so the fix would be “a fixed lookup table or a single if branch based on the date and the number of integers to add when doing the integer representation to human representation mathematics before updating the clock on your screen.

Re: Celestial Reference Frame Department

#35

Post by michaelmior »

techdragon wrote: post #19
ReactiveJelly wrote: post #6

Earlier quoted context omitted.

> These are the people behind leap seconds. So they are my enemies

You have been lied to… your true enemies are the ones that continue to build monotonic systems on top of non monotonic time scales… Join us in the Temps Atomic International! TAI is the one true timescale. Computers should be using TAI and converting to UTC when humans want to see a local human time. My sincere belief is this was a bigger mistake than null, bigger than all the Y2K “we stored the year as 2 digits” stu…

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

Re: Celestial Reference Frame Department

#36

Post by michaelmior »

RetroTechie wrote: post #26
techdragon wrote: post #19

Earlier quoted context omitted.

You have been lied to… your true enemies are the ones that continue to build monotonic systems on top of non monotonic time scales… Join us in the Temps Atomic International! TAI is the one true timescale. Computers should be using TAI and converting to UTC when humans want to see a local human time. My sincere belief is this was a bigger mistake than null, bigger than all the Y2K “we stored the year as 2 digits” stu…

> (..) but just infrequent enough almost everyone can ignore it ... If it's only a problem for the experts, then it isn't really a problem, right? The experts can decide for themselves how hard they work on solving self-invented problems.

> If it's only a problem for the experts, then it isn't really a problem, right?

I don't really follow this logic. There are lots of things that are only problems for experts because the experts solve the problem for everyone else.

Re: Celestial Reference Frame Department

#37

Post by techdragon »

michaelmior wrote: post #35
techdragon wrote: post #19

Earlier quoted context omitted.

You have been lied to… your true enemies are the ones that continue to build monotonic systems on top of non monotonic time scales… Join us in the Temps Atomic International! TAI is the one true timescale. Computers should be using TAI and converting to UTC when humans want to see a local human time. My sincere belief is this was a bigger mistake than null, bigger than all the Y2K “we stored the year as 2 digits” stu…

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 and how no one is precisely sure why that’s the version we got, spoilers: The English acronym and the French acronym both aren’t in the correct order for us to use the letters UTC, yet the acronym is UTC and no one is sure exactly why, like it may have been a compromise hashed out over drinks at some hotel bar between metrologists at a conference and written into the text that way without comment… it’s lost to history (at least the history I’ve been able to find when I ran down this rabbit hole)

Re: Celestial Reference Frame Department

#38

Post by jdougan »

hollander wrote: post #33
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 .

Think of what you can do as International Earth Rotation Manager! Probably not much, but what a job title!

I'd love that on a business card. Add a doodle of the Giant Lever, with a hand adjusting it...

Re: Celestial Reference Frame Department

#39

Post by fanf2 »

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.

That isn’t quite right.

UTC was originally (early 1960s) coordinated between the British and Americans. This was related to their existing collaborations in time and navigation. The definition of the atomic second was established in 1955-1958 by a collaboration between NPL (London) who had the first good atomic clock, and the USNO who were good at the astronometric work to establish the ephemeris second. The USNO and the Greenwich observatory also prepared the Astronomical Almanac together.

Later on, as other countries wanted to use the same atomic timescale, the BIH (bureau international de l’heure, based at the Paris observatory) took over. More recently, the BIH was split.

The part responsible for atomic time moved to the BIPM (bureau international des poids et mesures, in Sévres just outside Paris) who are responsible for the definition of the second, so it makes sense for them to be responsible for its realisation as well. They maintain atomic time based on contributions from many atomic clocks in many time labs around the world.

The astronomy parts of the BIH became the IERS (international earth rotation service), still based at the Paris Observatory. However, a significant part of their practical scientific work is carried out by the USNO. For instance IERS Bulletin A is sent out each week by the USNO. Earth orientation is needed for the GPS as well as for leap seconds.

Re: Celestial Reference Frame Department

#40

Post by fanf2 »

ReactiveJelly wrote: post #6
Animats wrote: post #5

Earlier quoted context omitted.

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...

> These are the people behind leap seconds. So they are my enemies

Most of the people responsible for implementing leap seconds want to get rid of them too. The international bureaucratic wheels are grinding slowly towards abolition: should be more successful this time than the previous attempt ~15-20 years ago.
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