Re: [time-nuts] Absolute time accuracy pre-Cesium?
Hi: I have a some what related question. I'm just curious how far back in time do the current time scales extend ? (Ie. When was the first "second hack / synchronization" that can be related to our current time.) Thanks in advance for any answers. Mark Spencer m...@alignedsolutions.com 604 762 4099 > On Mar 26, 2019, at 2:58 AM, 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 Dava Sobel's "Longitude") that he would look from the edge of his > window at a particular star each night and note (while counting the > ticks he heard from his clock) the exact moment it would disappear > behind a nearby chimney, and knowing the Earth's rotation takes four > minutes and some (I forget) seconds off from a day, he used this to > calibrate and test the precision and accuracy of his long clocks. It > was suggested he could get within less than second with this method. > This was around age 21, so the year would be about 1714. Looking > online for PZT (photographic zenith tube), I didn't find much about > it, but it was surely first made a couple centuries after this. > > The Sobel book (all about how Harrison won the Longitude prize) is > more a popular book and less technical, but "Quest" has many > mostly-technical articles, mostly about Harrison, as well as beautiful > photos of his clocks. One or two of the articles is by the man who > made (or made the parts for it, the story is complicated) the > one-second-in-100-days "Clock B" pendulum clock, built from Harrison's > writings and claims of just that accuracy in the book he wrote shortly > before his death. > >> On Mon, Mar 25, 2019 at 7:00 PM John Ackermann N8UR wrote: >> >> Does anyone have a pointer to information about the absolute time >> accuracy (not stability) that was available via PZT or other techniques >> prior to the Cesium definition? I'm doing a presentation and want to >> show the evolution of accuracy. My Google-fu has failed me in finding >> anything pre-Atomic. >> >> Thanks! >> John >> >> >> ___ >> 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?
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 Dava Sobel's "Longitude") that he would look from the edge of his >window at a particular star each night and note (while counting the >ticks he heard from his clock) the exact moment it would disappear >behind a nearby chimney, and knowing the Earth's rotation takes four >minutes and some (I forget) seconds off from a day, he used this to >calibrate and test the precision and accuracy of his long clocks. It >was suggested he could get within less than second with this method. >This was around age 21, so the year would be about 1714. Looking >online for PZT (photographic zenith tube), I didn't find much about >it, but it was surely first made a couple centuries after this. > >The Sobel book (all about how Harrison won the Longitude prize) is >more a popular book and less technical, but "Quest" has many >mostly-technical articles, mostly about Harrison, as well as beautiful >photos of his clocks. One or two of the articles is by the man who >made (or made the parts for it, the story is complicated) the >one-second-in-100-days "Clock B" pendulum clock, built from Harrison's >writings and claims of just that accuracy in the book he wrote shortly >before his death. > >On Mon, Mar 25, 2019 at 7:00 PM John Ackermann N8UR >wrote: >> >> Does anyone have a pointer to information about the absolute time >> accuracy (not stability) that was available via PZT or other >techniques >> prior to the Cesium definition? I'm doing a presentation and want to >> show the evolution of accuracy. My Google-fu has failed me in >finding >> anything pre-Atomic. >> >> Thanks! >> John >> >> >> ___ >> 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?
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 Dava Sobel's "Longitude") that he would look from the edge of his >>window at a particular star each night and note (while counting the >>ticks he heard from his clock) the exact moment it would disappear >>behind a nearby chimney, and knowing the Earth's rotation takes four >>minutes and some (I forget) seconds off from a day, he used this to >>calibrate and test the precision and accuracy of his long clocks. It >>was suggested he could get within less than second with this method. >>This was around age 21, so the year would be about 1714. Looking >>online for PZT (photographic zenith tube), I didn't find much about >>it, but it was surely first made a couple centuries after this. >> >>The Sobel book (all about how Harrison won the Longitude prize) is >>more a popular book and less technical, but "Quest" has many >>mostly-technical articles, mostly about Harrison, as well as beautiful >>photos of his clocks. One or two of the articles is by the man who >>made (or made the parts for it, the story is complicated) the >>one-second-in-100-days "Clock B" pendulum clock, built from Harrison's >>writings and claims of just that accuracy in the book he wrote shortly >>before his death. >> >>On Mon, Mar 25, 2019 at 7:00 PM John Ackermann N8UR >>wrote: >>> >>> Does anyone have a pointer to information about the absolute time >>> accuracy (not stability) that was available via PZT or other >>techniques >>> prior to the Cesium definition? I'm doing a presentation and want to >>> show the evolution of accuracy. My Google-fu has failed me in >>finding >>> anything pre-Atomic. >>> >>> Thanks! >>> John >>> >>> >>> ___
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 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 Dava Sobel's "Longitude") that he would look from the edge of his >>window at a particular star each night and note (while counting the >>ticks he heard from his clock) the exact moment it would disappear >>behind a nearby chimney, and knowing the Earth's rotation takes four >>minutes and some (I forget) seconds off from a day, he used this to >>calibrate and test the precision and accuracy of his long clocks. It >>was suggested he could get within less than second with this method. >>This was around age 21, so the year would be about 1714. Looking >>online for PZT (photographic zenith tube), I didn't find much about >>it, but it was surely first made a couple centuries after this. >> >>The Sobel book (all about how Harrison won the Longitude prize) is >>more a popular book and less technical, but "Quest" has many >>mostly-technical articles, mostly about Harrison, as well as beautiful >>photos of his clocks. One or two of the articles is by the man who >>made (or made the parts for it, the story is complicated) the >>one-second-in-100-days "Clock B" pendulum clock, built from Harrison's >>writings and claims of just that accuracy in the book he wrote shortly
Re: [time-nuts] Absolute time accuracy pre-Cesium?
Hi John: One of the papers from 1968 mentioned "continental drift" could be detected if two stations were at the same latitude, i.e. looking at the same set of stars. That was also the case for the Latitude Observatories which were all at 39:08. While they were setup with Zenith Telescopes optimized to measure the angle between plumb and a star near the Zenith, near the end some PZTs were tried and worked about the same. https://prc68.com/I/UkiahObs.shtml The observatory here in Ukiah, CA at first used a sidereal pendulum clock, but at the end it was using a Heathkit GC-100 clock. It was a big deal and so showed up in the local newspaper. https://prc68.com/I/HeathkitGC1000.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 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 Dava Sobel's "Longitude") that he would look from the edge of his window at a particular star each night and note (while counting the ticks he heard from his clock) the exact moment it would disappear behind a nearby chimney, and knowing the Earth's rotation takes four minutes and some (I forget) seconds off from a day, he used this to calibrate and test the precision and accuracy of his long clocks. It was suggested he could get within less than second with this method. This was around age 21, so the year would be about 1714. Looking online for PZT (photographic zenith tube), I didn't find much about it, but it was surely first made a couple centuries after this. The Sobel book (all about how Harrison won the Longitude prize) is more a popular book and less technical, but "Quest" has many mostly-technical articles, mostly about Harrison, as well as beautiful photos of his clocks. One or two of the articles is by the man who made (or made the parts for it, the story is complicated) the one-second-in-100-days "Clock B" pendulum clock, built from Harrison's writings and claims of just that accuracy in the book he wrote shortly before his death. On Mon, Mar 25, 2019 at 7:00 PM John Ackermann N8UR wrote: Does anyone have a pointer to information about the absolute time accuracy (not stability) that was available via PZT or other techniques prior to the Cesium definition? I'm doing a presentation and want to show the evolution of accuracy. My Google-fu has failed me in finding anything pre-Atomic. Thanks! John ___ 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.
[time-nuts] NAVICOM RCGD-M GPSDO
I recently picked up a NAVICOM RCGD-M GPSDO off of Ebay. Does anybody have any info on these? One version seems to have a Furuno GT08031, another seller show Lady Heather monitoring a Motorola 8 channel GPS, ___ 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
It must be a sign of the dedication that Harrison applied to his work. It is not as simple as the description first appears, this is England, and the method presupposes that there are no clouds. It might be a week or two before two nights occurred, when an unclouded night was followed by another night within several days that was not clouded. Similarly, with the longitude method, stars must be visible within a short period of dawn or dusk, when the horizon is visible together with the star. Sun sights are not so difficult. GPS makes is so easy for us! cheers, Neville Michie > On 27 Mar 2019, at 09:48, Bob Holmstrom wrote: > > Ben Bradley stated > "Perhaps closer to your question: I recall in my > readings about clockmaker John Harrison (likely either in "The Quest > for Longitude” or Dava Sobel's "Longitude") that he would look from > the edge of his window at a particular star each night and note (while > counting the ticks he heard from his clock) the exact moment it would > disappear behind a nearby chimney, and knowing the Earth's rotation > takes four minutes and some (I forget) seconds off from a day, he used > this to calibrate and test the precision and accuracy of his long > clocks. It was suggested he could get within less than second with > this method." > > From Sobel - Chapter 7 > "The Harrison brothers tested the accuracy of > their gridiron-grasshopper clocks against the regular motions of the > stars. The crosshairs of their homemade astronomical tracking > instrument, with which they pinpointed the stars' positions, consisted > of the border of a windowpane and the silhouette of the neighbor's > chimney stack. Night after night, they marked the clock hour when > given stars exited their field of view behind the chimney. From one > night to the next, because of the Earth's rotation, a star should > transit exactly 3 minutes, 56 seconds (of solar time) earlier than the > previous night. Any clock that can track this sidereal schedule proves > itself as perfect as God's magnificent clockwork.” > > 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. > Harrison would watch a single star (obviously the same star for > several nights) in the gap between the right vertical edge of a window > mullion and the left edge of his neighbors chimney. He would move his > eye so as to always keep the star in the gap. Eventually, the gap > closes to zero and the star ‘winks out’. At that point he would > verbally signal his assistant watching Harrison's clock pendulum tip > swinging against a degree scale below. Harrison’s grasshopper > escapement clocks had a very large amplitude (+/- several degrees) > compared to that used by precision clocks today, so it is said that > the assistant could record the results to a fraction of a second. > > Jonathan Betts has a description of the method in his “Harrison” > published by the National Maritime Museum in 2007 - see attachment. > > A pendulum clock is not required to verify the method - all that is > needed is a similar star sighting arrangement and a means to record > the time of the ‘wink out’ - preferably to a fraction of a second. > Subsequent night ‘wink out’ times should be 3 minutes, 56 seconds > apart. (Is that single value valid over a 400 years period?) > > Bob Holmström > Editor > Horological Science Newsletter > PM3.png>___ > 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
On 3/26/19 3:48 PM, Bob Holmstrom wrote: Ben Bradley stated > "Perhaps closer to your question: I recall in my readings about clockmaker John Harrison (likely either in "The Quest for Longitude” or Dava Sobel's "Longitude") that he would look from the edge of his window at a particular star each night and note (while counting the ticks he heard from his clock) the exact moment it would disappear behind a nearby chimney, and knowing the Earth's rotation takes four minutes and some (I forget) seconds off from a day, he used this to calibrate and test the precision and accuracy of his long clocks. It was suggested he could get within less than second with this method." From Sobel - Chapter 7 > "The Harrison brothers tested the accuracy of their gridiron-grasshopper clocks against the regular motions of the stars. The crosshairs of their homemade astronomical tracking instrument, with which they pinpointed the stars' positions, consisted of the border of a windowpane and the silhouette of the neighbor's chimney stack. Night after night, they marked the clock hour when given stars exited their field of view behind the chimney. From one night to the next, because of the Earth's rotation, a star should transit exactly 3 minutes, 56 seconds (of solar time) earlier than the previous night. Any clock that can track this sidereal schedule proves itself as perfect as God's magnificent clockwork.” 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. 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. A small telescope and a camera might work, lining up with the two edges as a "fixed offset knife edges". It could also work in day time (you can see Polaris in the day time with a 28x telescope with a 1" objective - a surveyor's theodolite) There's a collection of navigation papers from ION available on CD-ROM and there's a fair amount of info in there about celestial trackers and detectors. ___ 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
On 3/26/19 4:27 PM, Neville Michie wrote: It must be a sign of the dedication that Harrison applied to his work. It is not as simple as the description first appears, this is England, and the method presupposes that there are no clouds. It might be a week or two before two nights occurred, when an unclouded night was followed by another night within several days that was not clouded. Similarly, with the longitude method, stars must be visible within a short period of dawn or dusk, when the horizon is visible together with the star. Sun sights are not so difficult. You can use an artificial horizon (historically, a pool of mercury) and shoot the star and its reflection, then divide by two. I've used water reflection in a bowl to shoot the sun and moon, but those are really bright. I've not tried a star. It would be really hard in an area with background light because you'd have trouble dark adapting. You can fairly easily shoot moon and star together, though, to get an angle between star and moon's limb. Maybe you could float some aluminized mylar on the water surface to help the reflectivity. GPS makes is so easy for us! Until the batteries go dead. ___ 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
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.
Re: [time-nuts] reply re Harrison's timing method - #13 in Vol 176, Issue 44 digest
Greetings time-nuts, Harrison's method depends on the star having the same true azimuth at 1 Sidereal day intervals (23 hours 56 minutes 04 seconds). It does not depend on a visible horizon since the altitude (which changes with the season) is not relevant except that one must be able to see the star and the reference markers in the field of view. Star sights in marine navigation depend on the horizon being visible through the sextant because one is measuring the altitude of the star rather than its azimuth. Harrison's method does not depend on the time of observation being at dawn or dusk and will work in full darkness since the star "goes out" when its light is obstructed by the chimney and the light of a candle enables the window bar to be seen for fixing the position of the observer's eye. It does, however, depend on both the chimney and the window bar being vertical! Today one could repeat the experiment with, for example, a theodolite with two fixed positions (one for the theodolite itself and a remote one to be able to reset the theodolite to the same azimuth), or an Azimuth Circle and a Nautical Almanac, or an Observatory (for the more wealthy time-nuts!). Any repeatable method of determining the instant when the star is at a fixed azimuth will accurately provide the instant when the time is an integral number of sidereal days after the previous observation so a few days of cloud are of little consequence. Like most of Harrison's methods, this method is fundamentally sound and remarkably accurate. Best regards, Roger. On Wed, 27 Mar 2019 10:27:44 +1100, Neville Michie wrote: > It must be a sign of the dedication that Harrison applied to his work. > It is not as simple as the description first appears, this is England, > and the method presupposes that there are no clouds. It might be a week > or two before two nights occurred, when an unclouded night was followed > by another night within several days that was not clouded. > Similarly, with the longitude method, stars must be visible within a > short period of dawn or dusk, when the horizon is visible together with > the star. Sun sights are not so difficult. > GPS makes is so easy for us! > cheers, > > Neville Michie > > > On 27 Mar 2019, at 09:48, Bob Holmstrom wrote: > > > > Ben Bradley stated > "Perhaps closer to your question: I recall in my > > readings about clockmaker John Harrison (likely either in "The Quest > > for Longitude” or Dava Sobel's "Longitude") that he would look from > > the edge of his window at a particular star each night and note (while > > counting the ticks he heard from his clock) the exact moment it would > > disappear behind a nearby chimney, and knowing the Earth's rotation > > takes four minutes and some (I forget) seconds off from a day, he used > > this to calibrate and test the precision and accuracy of his long > > clocks. It was suggested he could get within less than second with > > this method." > > > > From Sobel - Chapter 7 > "The Harrison brothers tested the accuracy of > > their gridiron-grasshopper clocks against the regular motions of the > > stars. The crosshairs of their homemade astronomical tracking > > instrument, with which they pinpointed the stars' positions, consisted > > of the border of a windowpane and the silhouette of the neighbor's > > chimney stack. Night after night, they marked the clock hour when > > given stars exited their field of view behind the chimney. From one > > night to the next, because of the Earth's rotation, a star should > > transit exactly 3 minutes, 56 seconds (of solar time) earlier than the > > previous night. Any clock that can track this sidereal schedule proves > > itself as perfect as God's magnificent clockwork.” > > > > 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. > > Harrison would watch a single star (obviously the same star for > > several nights) in the gap between the right vertical edge of a window > > mullion and the left edge of his neighbors chimney. He would move his > > eye so as to always keep the star in the gap. Eventually, the gap > > closes to zero and the star ‘winks out’. At that point he would > > verbally signal his assistant watching Harrison's clock pendulum tip > > swinging against a degree scale below. Harrison’s grasshopper > > escapement clocks had a very large amplitude (+/- several degrees) > > compared to that used by precision clocks today, so it is said that > > the assistant could record the results to a fraction of a second. > > > > Jonathan Betts has a description of the method in his “Harrison” > > published by the National Maritime Museum in 2007 - see attachment. > > > > A pendulum clock is not required to verify the method - all that is > >
Re: [time-nuts] reply re Harrison's timing method - #13 in Vol 176, Issue 44 digest
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.
Re: [time-nuts] reply re Harrison's timing method - #13 in Vol 176, Issue 44 digest
On Wed 2019-03-27T16:26:09+1300 Bruce Griffiths hath writ: > The Danjon impersonal astrolabe is perhaps better suited to accurate > measurements: > https://www.nzmuseums.co.nz/collections/3267/objects/3380/astrolabe Danjon became director of Observatoire de Paris (and thus also the BIH) in 1945. In 1948 the ITU realized that it could not make reasonable regulations about frequency in the absence of an expert on timing, so ITU requested the IAU send a representative to Study Group 7, and Danjon was that representative. Danjon was head of the CCDS from inception into the late 1960s. The raw data about the clocks at Observatoire de Paris (which were located in the catacombs for temperature stability) from the 1920s into the quartz era are almost all published in Bulletin Horaire. The early issues are all scanned and online at Harvard ADS. That is a huge amount data on earth disciplined oscillators, a treasure chest of descriptions and diagrams of early circuits and drum recording devices, and a pile of dirty laundry about who made good and bad decisions in international agreements about time. -- Steve Allen WGS-84 (GPS) UCO/Lick Observatory--ISB 260 Natural Sciences II, Room 165 Lat +36.99855 1156 High Street Voice: +1 831 459 3046 Lng -122.06015 Santa Cruz, CA 95064 https://www.ucolick.org/~sla/ Hgt +250 m ___ 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
These light curves for a star being occulted by the moon should give some idea of the effects of diffraction: http://tdc-www.harvard.edu/occultations/moon/vb141occa.html 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.
