In answer to the question about radio astronomers, consider VLBI (Very Long Baseline Interferometry).
VLBI is a mapping (imaging) process in which signals are *simultaneously* received from a small sky region of interest by a collection of radio telescopes scattered about the world. In order for the process to work, ultimately it is necessary for all the signals to be lined up in time (think phase) to a small fraction of a period of the microwave frequency being used. Suppose the frequency is around 5 GHz, then the period is just 200 psec, and a small enough fraction thereof is maybe 10 psec or less. Now present day clocks and time transfer schemes are not good enough to accomplish that feat "open loop" across a collection of observatories spanning thousands of miles. Fortunately, radio astronomers have developed a set of magical techniques collectively called "self calibration" by which, with extreme care, the job can still be done provided that the data sets from each observatory are initially lined up to within around 100 nsec. However, another requirement is that the LOs for the different observatories' receivers maintain that constant phase relationship I mentioned above during the course of an observation. In practice this condition can typically only be held for a few minutes at a time, and the only atomic clock in commercial production that can do that is the hydrogen maser. Cs beam clocks are simply not stable enough in that time frame to get the job done. But I'm quite sure that much more stable clocks yet would relieve the overall problem of making much longer continuous observations. Not solve all aspects of the problem by itself, but it would sure help. Another use for such observations is earthbound geodesy, used to track continental drift and the like. Here the preferred radio source is a bright point source such as a quasar, and the point is monitoring the position of each observatory. In this application it's important to accurately know the position of the selected source, and one of the applications of VLBI is also to measure source locations. So if you're an astrophysicist you want to know the precise locations of all the telescopes, and uncertainty in this is "noise". But the person wanting geodesic information want to measure drift in telescope positions, and needs to know where the source is located in the sky. So one man's signal is the other man's noise, and vice versa. In any case, anything that can be done to improve phase coherence between all the receivers in the network can only help. Dana Previous "Keeper of The Clock" at the Arecibo Observatory in Puerto Rico On Tue, Jun 4, 2019 at 6:01 PM Poul-Henning Kamp <p...@phk.freebsd.dk> wrote: > -------- > In message <CANy2iXowYBPreNnbrjnU7_XLz=NJ5ZVaGVMT0PRmUD0= > 7bl...@mail.gmail.com> > , "William H. Fite" writes: > > >What I am asking is not the validity of the quest for better timing > >but rather its tangible applications. > > Tangible for who ? > > For the average pedestrian there are no *current* tangible applications > where cesium level time-keeping isn't plenty. > > However, the same would have been said about chronometers and quartz > clocks at various times in the past. > > To answer your question we would need to look about 20-30 years > into the future, which seems to be the median time for better > timekeeping to break through to the wider public, even if they do > not know it has happened, (ie: longitude navigation, digital telephone > networks, GPS. > > Peeking 20-30 years into the future is an unsolved problem, so I > would argue that your question is unanswerable at this time. > > -- > Poul-Henning Kamp | UNIX since Zilog Zeus 3.20 > p...@freebsd.org | TCP/IP since RFC 956 > FreeBSD committer | BSD since 4.3-tahoe > Never attribute to malice what can adequately be explained by incompetence. > > _______________________________________________ > time-nuts mailing list -- time-nuts@lists.febo.com > To unsubscribe, go to > http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com > and follow the instructions there. > _______________________________________________ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.