Re: [time-nuts] reply re Harrison's timing method - #13 in Vol 176, Issue 44 digest
In principle one could time tag each individual photon with subnanosecond resolution. Bruce > On 29 March 2019 at 09:00 Poul-Henning Kamp wrote: > > > > In message <236772484.9174006.1553757616...@webmail.xtra.co.nz>, Bruce > Griffith > s writes: > > >However when used with a CCD camera or equivalent the accuracy > >should improve somewhat much as adding a TV camera to a transit > >circle improved its accuracy. > > You know ... there *is* an official time-nut way to do this. > > You want is a chevron shaped 'Høg grid' because that is > objectively a very, very, very smart way of converting precise > time to precise geometry. > > I don't know of any popular explanations, but look at page 10 here: > > https://www.hs.uni-hamburg.de/DE/Ins/Bib/AG2012AK1.pdf > > The illustration on page 10 shows the original concept (from 1925!): > > By modulating the starlight with a non-uniform pattern, and sampling > the modulated light at high rate, the transit time of the star can > be determined on the order of the sampling frequency. > > Notice that the photon detector does not need high geometric resolution, > I belive Strømberg, 17 year old at the time, used a simple photo-cell > or possibly a photo-multiplier. > > Now, if you want to measure both coordinates, you move to the chevron > shaped grid illustrated on page 11, the "Høg grid". > > You still get a precise measurement of the transit along the logitudal > axis, but the width of the signal now also tells you where the star > was on the transverse axis. > > This is how the Perth 1970 catalog was made, and if not for a loose > bolt, it would have been the most precise catalog on both axis instead > of just one axis. > > The Høg grid still leaves rotation as source of error, so look at > page 2 here: > > > https://pdfs.semanticscholar.org/27f4/16df19441874fcd3b1bf52c477c889ca8045.pdf > > Imagine the light-curve you get when a star transits that slit system > in various directions, including, crucially, with a rotation[1]. > > About 12 years ago I did some ad-hoc experiements on my 5" telescope, > with various simple slit geometries, and it works a treat. > > I made the slits by taping mylar tape on a neutral filter, and cut > slits with a scalpel and a steel ruler, the detector was a large > area PIN photo-diode from the junk box and a digital oscilloscope. > > While you can prove the concept, as I did, with portable tripod > mount, to get usable data you have to bolt the telecope to a cubic > meter of concrete or bedrock. > > Poul-Henning > > [1] This becaue very important for the Hipparcos satelite which a > rocket failure left stranded in the parking orbit ... but they still > completed their science objectives. > > -- > 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.
Re: [time-nuts] GPS week rollover
Yo Mark! On Thu, 28 Mar 2019 20:38:42 + Mark Sims wrote: > I doubt that any GPS receivers will be newly affected on April 6. Telit has already issued an App note on this. They tested their GPS with a GPS simulator. One of their common models will fail on April 6. Two more will fail in November. Sorry, I can't find it online. I know because a well known self driving car company contacted me after they discovered a large number of their cars are affected. RGDS GARY --- Gary E. Miller Rellim 109 NW Wilmington Ave., Suite E, Bend, OR 97703 g...@rellim.com Tel:+1 541 382 8588 Veritas liberabit vos. -- Quid est veritas? "If you can’t measure it, you can’t improve it." - Lord Kelvin pgp7xfBehlVAP.pgp Description: OpenPGP digital signature ___ 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] GPS week rollover
I doubt that any GPS receivers will be newly affected on April 6. Some very early receivers were hit on the first GPS rollover, but those made since then usually have a 1024 week compensation built in based upon the firmware creation date. Those rollover 1024 weeks from that date and start sending incorrect dates at other places in the 1024 week cycle. Some receivers even let you force the rollover week. > I have a Z3816A that’s showing a yellow “ro” next to the date in LH and is 18 > seconds ahead of a Motorola 12 channel If Lady Heather sees a date earlier than a set year (currently 2017), it assumes the GPS device has rollover issues and adds 1024 weeks to correct the date and shows the "ro" flag. As far as the 18 second time difference, one of the devices is configured to show GPS time and the other is set for UTC time. At the top right corner of the screen it should say either "UTC time OK" or "GPS time OK" (as long as the device has a valid time). The TG and TU commands can switch between GPS and UTC time displays. Some receivers have firmware commands to switch between the two. For the others, Heather does the conversion in software using the "UTC offset" (i.e. leapsecond count) value. Many receivers send this offset. If it does not, the user can set the value. And if no value is available Heather makes a best guess as to what the value might be (and shows it in RED). The guessed value is rather prone to errors, but is better than nothing. ___ 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.
Re: [time-nuts] reply re Harrison's timing method - #13 in Vol 176, Issue 44 digest
Hi I randomly came across: Publications of the United States Naval Observatory January 1, 1900 U.S. Government Printing Office Which turns out to be a Google E-Book. It goes into some detail about just how the transit data contained in it was obtained. For the (free) price it’s worth taking a look at. Bob > On Mar 28, 2019, at 4:00 PM, Poul-Henning Kamp wrote: > > > In message <236772484.9174006.1553757616...@webmail.xtra.co.nz>, Bruce > Griffith > s writes: > >> However when used with a CCD camera or equivalent the accuracy >> should improve somewhat much as adding a TV camera to a transit >> circle improved its accuracy. > > You know ... there *is* an official time-nut way to do this. > > You want is a chevron shaped 'Høg grid' because that is > objectively a very, very, very smart way of converting precise > time to precise geometry. > > I don't know of any popular explanations, but look at page 10 here: > > https://www.hs.uni-hamburg.de/DE/Ins/Bib/AG2012AK1.pdf > > The illustration on page 10 shows the original concept (from 1925!): > > By modulating the starlight with a non-uniform pattern, and sampling > the modulated light at high rate, the transit time of the star can > be determined on the order of the sampling frequency. > > Notice that the photon detector does not need high geometric resolution, > I belive Strømberg, 17 year old at the time, used a simple photo-cell > or possibly a photo-multiplier. > > Now, if you want to measure both coordinates, you move to the chevron > shaped grid illustrated on page 11, the "Høg grid". > > You still get a precise measurement of the transit along the logitudal > axis, but the width of the signal now also tells you where the star > was on the transverse axis. > > This is how the Perth 1970 catalog was made, and if not for a loose > bolt, it would have been the most precise catalog on both axis instead > of just one axis. > > The Høg grid still leaves rotation as source of error, so look at > page 2 here: > > > https://pdfs.semanticscholar.org/27f4/16df19441874fcd3b1bf52c477c889ca8045.pdf > > Imagine the light-curve you get when a star transits that slit system > in various directions, including, crucially, with a rotation[1]. > > About 12 years ago I did some ad-hoc experiements on my 5" telescope, > with various simple slit geometries, and it works a treat. > > I made the slits by taping mylar tape on a neutral filter, and cut > slits with a scalpel and a steel ruler, the detector was a large > area PIN photo-diode from the junk box and a digital oscilloscope. > > While you can prove the concept, as I did, with portable tripod > mount, to get usable data you have to bolt the telecope to a cubic > meter of concrete or bedrock. > > Poul-Henning > > [1] This becaue very important for the Hipparcos satelite which a > rocket failure left stranded in the parking orbit ... but they still > completed their science objectives. > > -- > 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.
Re: [time-nuts] reply re Harrison's timing method - #13 in Vol 176, Issue 44 digest
In message <236772484.9174006.1553757616...@webmail.xtra.co.nz>, Bruce Griffith s writes: >However when used with a CCD camera or equivalent the accuracy >should improve somewhat much as adding a TV camera to a transit >circle improved its accuracy. You know ... there *is* an official time-nut way to do this. You want is a chevron shaped 'Høg grid' because that is objectively a very, very, very smart way of converting precise time to precise geometry. I don't know of any popular explanations, but look at page 10 here: https://www.hs.uni-hamburg.de/DE/Ins/Bib/AG2012AK1.pdf The illustration on page 10 shows the original concept (from 1925!): By modulating the starlight with a non-uniform pattern, and sampling the modulated light at high rate, the transit time of the star can be determined on the order of the sampling frequency. Notice that the photon detector does not need high geometric resolution, I belive Strømberg, 17 year old at the time, used a simple photo-cell or possibly a photo-multiplier. Now, if you want to measure both coordinates, you move to the chevron shaped grid illustrated on page 11, the "Høg grid". You still get a precise measurement of the transit along the logitudal axis, but the width of the signal now also tells you where the star was on the transverse axis. This is how the Perth 1970 catalog was made, and if not for a loose bolt, it would have been the most precise catalog on both axis instead of just one axis. The Høg grid still leaves rotation as source of error, so look at page 2 here: https://pdfs.semanticscholar.org/27f4/16df19441874fcd3b1bf52c477c889ca8045.pdf Imagine the light-curve you get when a star transits that slit system in various directions, including, crucially, with a rotation[1]. About 12 years ago I did some ad-hoc experiements on my 5" telescope, with various simple slit geometries, and it works a treat. I made the slits by taping mylar tape on a neutral filter, and cut slits with a scalpel and a steel ruler, the detector was a large area PIN photo-diode from the junk box and a digital oscilloscope. While you can prove the concept, as I did, with portable tripod mount, to get usable data you have to bolt the telecope to a cubic meter of concrete or bedrock. Poul-Henning [1] This becaue very important for the Hipparcos satelite which a rocket failure left stranded in the parking orbit ... but they still completed their science objectives. -- 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.
Re: [time-nuts] Yet another GPSDO project.
Tobias Pluess writes: > I once tried to use the internal PLL of the microcontroller to boost > the OCXO frequency to the max. 72 MHz which my microcontroller > accepts. While this would greatly increase the frequency measurement > resolution, it decreased stability because it appeared that the PLL > had some frequency modulation at its output. It's highly likely that the PLL on that micro is using a fractional divider (it probably tells you somewhere in the documentation). > I just tested different PLL multiplication factors, and according to > my tests, the stability of the PLL improves quite a bit if a power of > 2 multiplication factor is used, e.g. if the OCXO's 10MHz are > multiplied to 20 MHz or to 40 MHz. Yes, you'll have the best chances of getting the result you want with an integer ratio and for some implementations of the divider it should be either an even number or if you are really unlucky, a power of 2. In your case it might be possible to overclock the micro to 80MHz or, if even number ratios are OK, at least use 60MHz. It may be better to first divide the 10MHz down by two (the input circuit in the PLL might have a dedicated divider for doing that) and then multiply up to 60MHz or 70MHz with a ratio of 12 or 14. Regards, Achim. -- +<[Q+ Matrix-12 WAVE#46+305 Neuron microQkb Andromeda XTk Blofeld]>+ SD adaptations for KORG EX-800 and Poly-800MkII V0.9: http://Synth.Stromeko.net/Downloads.html#KorgSDada ___ 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.
Re: [time-nuts] GPS week rollover
I have a Z3816A that’s showing a yellow “ro” next to the date in LH and is 18 seconds ahead of a Motorola 12 channel (and my iPhone). I haven’t had time to look into it as I’m adjusting to “voluntary” retirement and trying to clear out some excess stuff. Steve > On Mar 28, 2019, at 1:30 PM, wrote: > > Are we expecting any week rollover problems with the receivers we time > nuts like to play with??? > > Cheers, > > Corby > > > ___ > 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.
[time-nuts] GPS week rollover
Are we expecting any week rollover problems with the receivers we time nuts like to play with??? Cheers, Corby ___ 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.
Re: [time-nuts] Yet another GPSDO project.
Sure. However my OCXO has around -155 dBc/Hz, almost 20dB worse than your -170. One channel of my distributor can be seen here https://hb9fsx.ch/wordpress/wp-content/uploads/2018/11/ad9631-10MHz-driver.png they have 200 Ohms input impedance and 4 of them are in parallel, so in total the input impedance to the distributor is 50 Ohms again for the OCXO. Tobias HB9FSX From: time-nuts [time-nuts-boun...@lists.febo.com] on behalf of Bob kb8tq [kb...@n1k.org] Sent: Thursday, March 28, 2019 02:01 To: Discussion of precise time and frequency measurement Subject: Re: [time-nuts] Yet another GPSDO project. Hi How much impact your distribution setup has on the OCXO phase noise depends a *lot* on how quiet the OCXO is. If it is in the -170 dbc/ Hz range, then pretty much anything can mess up the phase noise …. Bob > On Mar 27, 2019, at 5:05 PM, Tobias Pluess wrote: > > Hi Leo, > > sorry for my late reply. > I have not yet measured the phase noise of my finished unit, since I am still > waiting to complete my phase noise measurement equipment. > However, I have a decent test report for my OCXO, where the phase noise > spectrum is also plotted. I don't expect my distributor circuit which I > connected to the OCXO to degrade the phase noise too much since it is just a > bunch of OpAmps and resistors. > I have a HP 8663A here for comparison, but I still lack a proper phase noise > test set. > > Tobias > > > > From: time-nuts [time-nuts-boun...@lists.febo.com] on behalf of Leo Bodnar > [l...@leobodnar.com] > Sent: Thursday, March 21, 2019 09:14 > To: time-nuts@lists.febo.com > Subject: Re: [time-nuts] Yet another GPSDO project. > > Tobias, > Have you measured resulting phase noise of the finished unit? > Thanks > Leo > >> From: Tobias Pluess >> sure, I believe you since my primary requirement was phase noise. This is >> because I'd like to use the OCXO as reference for my spectrum analyzer and >> also for my HP 8663 signal generator to do phase noise measurements > ___ > 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. ___ 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.
Re: [time-nuts] Absolute time accuracy pre-Cesium?
Bob, Physicists are still debating whether time is continuous or granular. One current theory of granularity uses the Planck Time, the time required for a photon traveling at c, the speed of light in a vacuum, to travel a Planck Length. This turns out to be 5.39x10^-44 seconds. This is small enough that, for the moment at least, even Time Nuts can treat time as continuous. Francis Grosz - Original Message --- Message: 1 Date: Tue, 26 Mar 2019 15:46:55 + (UTC) From: Bob Albert To: Discussion of precise time and frequency measurement Subject: Re: [time-nuts] Absolute time accuracy pre-Cesium? Message-ID: <1289017299.10285197.1553615215...@mail.yahoo.com> Content-Type: text/plain; charset=UTF-8 I have been pondering something somewhat related to all of this. We know that the smallest unit of a substance is a molecule.? The smallest unit of charge is maybe an electron.? So what could one imagine the smallest unit of time to be?? Is time digital in the nanoscale, or is it always an analog measurement?? Or, more fundamentally, is is just a concept rather than a reality? Bob ___ 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.
Re: [time-nuts] Absolute time accuracy pre-Cesium?
Hi TIme is “just a number”, it has no inherent granularity. If you need to measure at the 10^-?? level, the units will not be the problem. Coming up with a device that provides 10^-15 or 10^-18 sort of stability (let alone accuracy …. yikes ….) would take a pretty big limit on your charge card. Bumping the number an order of magnitude is the sort of thing that keeps an entire generation of staff at some pretty big national labs employed. That said, there have been some papers over the years about “what will you run into and when will you run into it?”. At some point gravity noise from “stuff” moving around gets into the picture and you need to move your clock into deep space ….. there *is* a number and for how much you walking across the room changes the gravity on your clock …. Needless to say, there are a lot of other things to worry about before that is the limit you worry about. Bob > On Mar 26, 2019, at 11:46 AM, Bob Albert via time-nuts > wrote: > > I have been pondering something somewhat related to all of this. > We know that the smallest unit of a substance is a molecule. The smallest > unit of charge is maybe an electron. So what could one imagine the smallest > unit of time to be? Is time digital in the nanoscale, or is it always an > analog measurement? Or, more fundamentally, is is just a concept rather than > a reality? > Bob >On Tuesday, March 26, 2019, 7:00:45 AM PDT, Kevin Birth > wrote: > > It all depends on how far back you want to go. With mechanical > timepieces, even before the pendulum there was Jost Burgi¹s astronomical > clock which achieved a precision of a second, and is reported to have been > accurate to that level based on astronomical measurements. Tycho Brahe > tried to achieve accuracy through using multiple clocks. This technique > actually seems to have been developed before Brahe with potentates like > Charles V having large numbers of clocks that he tried to synchronize. > There is at least one case of a Holy Roman Emperor with a bundle of clocks > getting angry at a clockmaker for having sold him a poor performing > clock‹that was Rudolf II. > > Before that you have some of the great Islamic observatories that measured > time with very large instruments. Here is a link, even without a > knowledge of Arabic, one can get a sense from the pictures how these > Muslim astronomers used scale to achieve great accuracy and precision. > What limited them were their materials‹at a certain scale their > instruments started to warp under their own weight. Many of the > principles in these instruments were based on Ptolemy¹s ALMAGEST, which > takes things back to the 3rd century AD or so. > > Here¹s the link: > https://gallica.bnf.fr/ark:/12148/btv1b8414999t.r=taqi%20al-din%20instrumen > ts?rk=21459;2 > > Before that the most detailed account of time measurement equipment is in > Vitruvius¹ work on architecture, but Vitruvius¹ descriptions are often > garbled, so there is no good way to judge their accuracy in relationship > to their claims of precision. > > Less well documented are Persian and South Asian methods in which the > smallest unit translates to something like the duration of a blink of an > eye. I do not know enough about those traditions to know what > observational methods or instruments they used to measure such a unit > (other than blinking a lot). > > Best, > > Kevin > > > -- > Kevin K. Birth, Professor > Department of Anthropology > Queens College, City University of New York > 65-30 Kissena Boulevard > Flushing, NY 11367 > telephone: 718/997-5518 > > "Tempus est mundi instabilis motus, rerumque labentium cursus." --Hrabanus > Maurus > > "We may live longer but we may be subject to peculiar contagion and > spiritual torpor or illiteracies of the imagination" --Wilson Harris > > > > > On 3/26/19, 7:30 AM, "time-nuts on behalf of John Ackermann. N8UR" > wrote: > >> EXTERNAL EMAIL: please report suspicious content to the ITS Help Desk. >> >> >> All -- thanks much for all the great references! I am giving the preso >> this afternoon (to a bunch of university space science students) so this >> will be a big help. And it looks like there's a lot of great reading for >> when I have time to breathe. >> >> Thanks again. >> John >> >> On Mar 25, 2019, 10:03 PM, at 10:03 PM, Ben Bradley >> wrote: >>> For independent standards (not quite what you asked) I recall from >>> "The Science of Clocks and Watches" (a book with much technical info >>> if you're interested in these mechanical devices) that the most >>> accurate mechanical/pendulum clock was the Shortt Clock that used a >>> pendulum in a vacuum chamber for its standard. Mechanical clocks were >>> replaced by more stable electronic quartz crystal oscillators, and >>> then finally by atomic clocks. >>> >>> Perhaps closer to your question: I recall in my readings about >>> clockmaker John Harrison (likely either in "The Quest for Longitude" >>> or
Re: [time-nuts] Absolute time accuracy pre-Cesium?
Read Book IV of Aristotle’s PHYSICS, take two aspirin then use all the instructions in the Islamic Hadith to know when it is really morning in order to call me in the morning :) Aristotle worried a lot about whether the measurement of time is conflated with time itself. We can reckon time using both analog and digital representations, but once we start wondering what the relationship of our representations are to what time is, we’re in deep philosophical waters. That said, Western metrology has tended toward emphasizing the usefulness of uniform units of measure. This has encouraged a trend towards viewing time as digital. Other cultural traditions view time as analog, and instead of reckoning time in terms of units of duration, reckon it in terms of points on a continuum of time. Hence my reference to the Hadith (the commentaries on the Qur’an). In the Hadith, it is very important to identify particular moments when one absolutely may not pray (e.g., the exact moment of sunrise). Its techniques for reckoning time are focused on knowing when particular moments are approaching. So I guess I’m saying that whether time is analog or digital depends on culture. But then again, I’m a cultural anthropologist, so that’s what I get paid to say. Best, Kevin -- Kevin K. Birth, Professor Department of Anthropology Queens College, City University of New York 65-30 Kissena Boulevard Flushing, NY 11367 telephone: 718/997-5518 "Tempus est mundi instabilis motus, rerumque labentium cursus." --Hrabanus Maurus "We may live longer but we may be subject to peculiar contagion and spiritual torpor or illiteracies of the imagination" --Wilson Harris On 3/26/19, 11:46 AM, "time-nuts on behalf of Bob Albert via time-nuts" wrote: >EXTERNAL EMAIL: please report suspicious content to the ITS Help Desk. > > > I have been pondering something somewhat related to all of this. >We know that the smallest unit of a substance is a molecule. The >smallest unit of charge is maybe an electron. So what could one imagine >the smallest unit of time to be? Is time digital in the nanoscale, or is >it always an analog measurement? Or, more fundamentally, is is just a >concept rather than a reality? >Bob >On Tuesday, March 26, 2019, 7:00:45 AM PDT, Kevin Birth > wrote: > > It all depends on how far back you want to go. With mechanical >timepieces, even before the pendulum there was Jost Burgi¹s astronomical >clock which achieved a precision of a second, and is reported to have been >accurate to that level based on astronomical measurements. Tycho Brahe >tried to achieve accuracy through using multiple clocks. This technique >actually seems to have been developed before Brahe with potentates like >Charles V having large numbers of clocks that he tried to synchronize. >There is at least one case of a Holy Roman Emperor with a bundle of clocks >getting angry at a clockmaker for having sold him a poor performing >clock‹that was Rudolf II. > >Before that you have some of the great Islamic observatories that measured >time with very large instruments. Here is a link, even without a >knowledge of Arabic, one can get a sense from the pictures how these >Muslim astronomers used scale to achieve great accuracy and precision. >What limited them were their materials‹at a certain scale their >instruments started to warp under their own weight. Many of the >principles in these instruments were based on Ptolemy¹s ALMAGEST, which >takes things back to the 3rd century AD or so. > >Here¹s the link: >https://gallica.bnf.fr/ark:/12148/btv1b8414999t.r=taqi%20al-din%20instrume >n >ts?rk=21459;2 > >Before that the most detailed account of time measurement equipment is in >Vitruvius¹ work on architecture, but Vitruvius¹ descriptions are often >garbled, so there is no good way to judge their accuracy in relationship >to their claims of precision. > >Less well documented are Persian and South Asian methods in which the >smallest unit translates to something like the duration of a blink of an >eye. I do not know enough about those traditions to know what >observational methods or instruments they used to measure such a unit >(other than blinking a lot). > >Best, > >Kevin > > >-- >Kevin K. Birth, Professor >Department of Anthropology >Queens College, City University of New York >65-30 Kissena Boulevard >Flushing, NY 11367 >telephone: 718/997-5518 > >"Tempus est mundi instabilis motus, rerumque labentium cursus." --Hrabanus >Maurus > >"We may live longer but we may be subject to peculiar contagion and >spiritual torpor or illiteracies of the imagination" --Wilson Harris > > > > >On 3/26/19, 7:30 AM, "time-nuts on behalf of John Ackermann. N8UR" > wrote: > >>EXTERNAL EMAIL: please report suspicious content to the ITS Help Desk. >> >> >>All -- thanks much for all the great references! I am giving the preso >>this afternoon (to a bunch of university space science students) so this >>will be a big help. And it looks like there's a lot of great
Re: [time-nuts] Absolute time accuracy pre-Cesium?
> I have been pondering something somewhat related to all of this. JohnA started and then concluded this thread about pre-Cesium time accuracy. Musings about quantized time gets pretty far off-topic for time-nuts. A couple of delayed postings from the queue will follow. But please, lets not go down a Planck rabbit hole here on time-nuts. Unless someone really knows, we'll call the thread closed. /tvb - Original Message - From: "Bob Albert via time-nuts" To: "Discussion of precise time and frequency measurement" Cc: "Bob Albert" Sent: Tuesday, March 26, 2019 8:46 AM Subject: Re: [time-nuts] Absolute time accuracy pre-Cesium? > I have been pondering something somewhat related to all of this. > We know that the smallest unit of a substance is a molecule. The smallest > unit of charge is maybe an electron. So what could one imagine the smallest > unit of time to be? Is time digital in the nanoscale, or is it always an > analog measurement? Or, more fundamentally, is is just a concept rather than > a reality? > Bob ___ 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.
Re: [time-nuts] reply re Harrison's timing method - #13 in Vol 176, Issue 44 digest
Brooke Yes but the accuracy would suffer due to observer related effects. However when used with a CCD camera or equivalent the accuracy should improve somewhat much as adding a TV camera to a transit circle improved its accuracy. I had a personal tour of the USNO setup on Black- Birch/Altimarloch during their southern hemisphere campaign during the 1980's. Bruce > On 27 March 2019 at 20:39 Brooke Clarke wrote: > > > Hi Bruce: > > Would the David White 60 Degree Pendulum Astrolabe also work? > https://prc68.com/I/PendulumAstrolabe.shtml > > -- > Have Fun, > > Brooke Clarke > https://www.PRC68.com > http://www.end2partygovernment.com/2012Issues.html > axioms: > 1. The extent to which you can fix or improve something will be limited by > how well you understand how it works. > 2. Everybody, with no exceptions, holds false beliefs. > > Original Message > > The Danjon impersonal astrolabe is perhaps better suited to accurate > > measurements: > > https://www.nzmuseums.co.nz/collections/3267/objects/3380/astrolabe > > > > Bruce > >> On 27 March 2019 at 15:48 Tom Van Baak wrote: > >> > >> > >> BobH wrote: > This would be an excellent project for time-nuts to verify. First, a > better explanation of John Harrison’s method is in order. A vertical > window edge is not sufficient - a second vertical reference at a > distance is required - Harrison used a chimney on a neighbor's house. > >> Agreed! The project is the perfect intersection of amateur astronomy and > >> amateur timekeeping. Surely, a couple of people on the list could 1) > >> attempt to verify the Harrison method, and 2) determine what the limits of > >> its accuracy are, say, with little effort vs. with hard work vs. with > >> extreme dedication. > >> > >> JimL wrote: > >>> To get 1 second accuracy, you need 360/86400 = 0.004 degree > >>> measurements. That's 0.073 milliradian - 1 cm at 140 meter distance. > >>> > >>> I'm not sure an "edge" is sharp enough (diffraction, etc.), although > >>> your eye is pretty good at "deconvolving" the linear equivalent of an > >>> Airy disk/rings. > >> Keep in mind too that one can take more than one star reading per night. > >> Any identifiable star that crosses your edge is a recordable timing event > >> that evening. So, in theory, if you measure N stars you get sqrt(N) > >> improvement in accuracy per day. > >> > >> I want to encourage anyone to study the problem and help solve the riddle, > >> either by uncovering existing professional or amateur literature or by > >> actually trying this at home. It boils down to how accurately can you > >> measure earth rotation using the Harrison method. > >> > >> To put this in time nuts context, precision timekeeping prior to the > >> middle of the 20th century was always a form of "Earth Disciplined > >> Oscillator". Not unlike a GPSDO, your observatory's pendulum clock kept > >> accurate time short-term and star tracking (earth rotation) kept accurate > >> time long-term. The ADEV's crossed just like a GPSDO. > >> > >> The short-term ADEV of a really good pendulum clock is here: > >> > >> http://leapsecond.com/pend/shortt/ > >> > >> The long-term ADEV of earth rotation is here: > >> > >> http://leapsecond.com/museum/earth/ > >> > >> So the performance of a DIY earth disciplined oscillator would be a > >> combination of the two. > >> > >> /tvb > >> > >> > >> ___ > >> 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. > > > > > ___ 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.
