Sundial on Mars
Toronto Astronomer, Andrew Yee, has advised: The Planetary Society (founded by Carl Sagan) in Pasadena, Calif. is soliciting ideas on sending a sundial to Mars on the 2001 Mars mission. See:http://planetary.org/news/hot-top-sundial.html . Tom Semadeni 45.768* North 80.600* West
Re: Stone Carving
The topic of the readability of shadows has again emerged. Some time ago there were some very scholarly postings that totally intimidated me. What are the empirical data to maximize legibility? color? roughness? distance from style? The simple things that the dialist can control? Many thanks for your help. Tom Semadeni 45.768* North 80.600* West
Re: Heliochronometers: Equation of Time
Chris Lusby's post is instructive and I'd like to learn more. Chris Lusby wrote: > It is true that tables of the Equation of Time are slightly inaccurate > > because they take a mean value for the solar longitude on a named date > (such > as February 17th), whereas the 4 year and 400 year cycles should be > allowed-for to be totally accurate. Fortunately for us, the peak error > is > less in the next few years than at any other time in the 400 year > cycle. How > convenient. The worst case is in 1903+400n and 2096+400n, when the > longitude > is 7/8 of a day different from its mean value. But even 7/8 of a day > accounts for less than 30 seconds of EoT, so still allows a sundial to > be > less than a minute out. Around the year 2000, the worst case is half > this - > about 14 seconds. Where do the 1903 and 2096 come from? Am I correct in assuming that ALL of the EoT discrepancy above comes from the (longitude-mean day) delta? > But if the sundial is marked with figure-of-eight hour lines, then > there > need be no such error, since the sun's declination and longitude are > related > by geometry, not by what we call the date. Even if we lost another 11 > days > in a calendar reform (I am from England), such a sundial would > continue to > read correct mean time. Therefore, I suggest that this is a purer and > altogether more satisfactory solution than an EoT table or figure. > Except > for the little point that the EoT changes rather a lot, and the > longitude > does not, at the solstices. Pity. I often see the figure-of-eight hour lines and don't understand why just one along the noon hour line isn't used. Is it only the practical matter that the observer isn't "there" at noon when he/she is observing at say 3pm? Or can the noon observation NOT be used to "calibrate" the observations for the rest of the day, at least? Thanks for your help t -- Tom Semadeni O [EMAIL PROTECTED] o aka I (Ned) Ames . Britthome Bounty ><<*> Box 176 Britt ON P0G 1A0 'Phone 705 383 0195 fax 2920 45.768* North 80.600* West
Re: Equation of Time
Thanks to Chris, for the clever graphical explanation showing especially the discontinuities which support his recommendation to look at John Shepherd's work on the beautifully designed and executed Richard D. Swensen Sundial at the University of Wisconsin - River Falls. http://www.uwrf.edu/sundial/ Not only is the sundial elegant, the web pages are too! The continuity of the analemma seems to respect Earth's rotation and revolution with much more fidelity than tables which give the "accuracy" of the dial by cataloguing the EoT with the (usually) Gregorian Calendar. That is to say the "in situ" analemmae prevent the inaccuracies introduced by the "calendar problem" that Chris illustrates so clearly. The only place where the "calendar problem" rears its ugly head on Shepherd's dial is on the week indicators on the analemmae themselves. Too bad, eh? (That's the Canuck coming out, eh! ) The Standard Time vs Daylight Time problem is neatly avoided. Precision: The close-up photographs clearly show the precision of this Sundial (or heliochronometer [sun-time-measurer], I guess), indicating an optimized diameter for the gnomon. Perhaps Professor Shepherd would care to share his thinking on the topic of precision with us. Analemmae: It appears that the calculations were done in general; then the location, scale and orientation variables were set in; resulting in some sort of output that was used as input into a CAD program; which in turn gave those beautiful analemmae which were then "pasted" onto the wall using another scaling factor. Perhaps Professor Shepherd would describe how he went from those terrible recursive functions which produce the EoT to getting a template for those analemmae. Thank you. -- Tom Semadeni O [EMAIL PROTECTED] o aka I (Ned) Ames . Britthome Bounty ><<*> Box 176 Britt ON P0G 1A0 'Phone 705 383 0195 fax 2920 45.768* North 80.600* West
Re: Heliochronometers: Equation of Time
Luke Coletti wrote: > Hello, > > I have found the best method of correcting for the periodic > variability > of the EoT relative to the calendar is to take the EoT as a four year > average. How do you do that? Do you pick a 12 month year which straddles the mid point between two leap years, like Jun 30, 97 to Jun 30, 98? Or do you calculate the "average" of something(s) and if so what? Perhaps the average of the 4 results of the noon EoT's for each day of the year. I.E., calculate the average of the noon results of the EoT for Jan 1,96; Jan 1,97; Jan 1,98 and Jan 1,99. Then do this for every day of the year and list the average across every day. Leap day? Or, is there a clever way of just "slipping" one day in the tabular values between the results of the EoT and the calendar day 4 times and then averaging. This would seem to work and the algorithm wouldn't be too daunting. > The temporal variability, as has been discussed in earlier > threads, is chiefly due to the phase relation between obliquity and > eccentricity as caused by the precession of the equinoxes and the > shifting of perihelion. The magnitude of obliquity and eccentricity > changes too but on a slower time scale. Does this mean that the daily values in the EoT, irrespective of the "calendar problem", generate some sort of periodic function when taken over the Period of a Year (of what sort?) but not quite? That is, on the anniversaries the EoT isn't quite where it was a Year ago due to the slow change in the absolute values of the obliquity and eccentricity? I missed the earlier thread that you referred to. Perhaps you could direct me to an URL which quantifies your two marvellously concise sentences above. I think that I'm getting in over my head and need to do some figuring! Thank you Tom Semadeni > > > Best Regards, > > Luke Coletti > > Chris Lusby wrote: > > > > Daniel Wegner ([EMAIL PROTECTED]) is only partly correct in > > saying that an analemma must have an error due to leap years. The error can > > be avoided. > > > > It is true that tables of the Equation of Time are slightly inaccurate > > because they take a mean value for the solar longitude on a named date (such > > as February 17th), whereas the 4 year and 400 year cycles should be > > allowed-for to be totally accurate. Fortunately for us, the peak error is > > less in the next few years than at any other time in the 400 year cycle. How > > convenient. The worst case is in 1903+400n and 2096+400n, when the longitude > > is 7/8 of a day different from its mean value. But even 7/8 of a day > > accounts for less than 30 seconds of EoT, so still allows a sundial to be > > less than a minute out. Around the year 2000, the worst case is half this - > > about 14 seconds. > > If an EoT table is drawn graphically to allow a sundial reading to be > > converted to mean time, then this too must have an error with the same 4 and > > 400 year cycles. > > > > But if the sundial is marked with figure-of-eight hour lines, then there > > need be no such error, since the sun's declination and longitude are related > > by geometry, not by what we call the date. Even if we lost another 11 days > > in a calendar reform (I am from England), such a sundial would continue to > > read correct mean time. Therefore, I suggest that this is a purer and > > altogether more satisfactory solution than an EoT table or figure. Except > > for the little point that the EoT changes rather a lot, and the longitude > > does not, at the solstices. Pity. > > > > By the way, if you are ever making a circular date scale - to calibrate a > > declination scale, for instance - you should divide it into 365.25 and make > > February 29th be just the .25. This is the best simple way to allow for one > > February 29th every four years. > > > > Chris Lusby Taylor > > > > === > > Email: [EMAIL PROTECTED] > > (Formerly [EMAIL PROTECTED]) > > === -- Tom Semadeni O [EMAIL PROTECTED] o aka I (Ned) Ames . Britthome Bounty ><<*> Box 176 Britt ON P0G 1A0 'Phone 705 383 0195 fax 2920 45.768* North 80.600* West
[Fwd: Equation of Time]
Oops, I neglected to post this to the list. Sorry, John. t -- Tom Semadeni O [EMAIL PROTECTED] o aka I (Ned) Ames . Britthome Bounty ><<*> Box 176 Britt ON P0G 1A0 'Phone 705 383 0195 fax 2920 45.768* North 80.600* West X-Mozilla-Status2: Message-ID: <[EMAIL PROTECTED]> Date: Sat, 20 Feb 1999 12:24:11 -0500 From: Tom Semadeni <[EMAIL PROTECTED]> Reply-To: [EMAIL PROTECTED] Organization: Britthome Bounty X-Mailer: Mozilla 4.5 (Macintosh; I; PPC) X-Accept-Language: en MIME-Version: 1.0 To: John Shepherd <[EMAIL PROTECTED]> Subject: Re: Equation of Time References: <[EMAIL PROTECTED]> <[EMAIL PROTECTED]> Content-Type: text/plain; charset=us-ascii; x-mac-type="54455854"; x-mac-creator="4D4F5353" Content-Transfer-Encoding: 7bit Thanks, John for telling of the situation which led to tha Aha! of the pointed double gnomon. The eye's extrapolation of the two shadows removes so much of the uncertainty caused by the geometrical and physical optics of the formation of the shadow. John Shepherd wrote: > With a vertical sundial at our latitude (45 degrees N) the shadow length > varies considerably and therefore so does the distance moved by the shadow > on the wall in a minute. So unless we were to vary the width of the bar > making the annalemmas (very costly) we had to chose a compromise for this > width and that of the pipes for the . The main factor turned out to be > visibility of the shadow and the annalemmas. We hung bar stock on the wall > and just looked at it from different distances:-) 1.25 by 0.75 inch turned > out to be best. Similarly we tried various pipes for the gnomon with > various terminations. When we viewed at the extreme hours we found the > discs and cross pieces on the end were too blured to see, hence the double > gnomon was born:-) snip > Actually as a Physicist part Astronomer the calculations were done first > using the Ephemeris Tables to calculate the Right Ascension/Declination of > the Sun at each hour for each day from this the direction of the Sun was > calculated for any latitude longitude and hence the intersection of the > shadow with the plane was found. Later I used "Compact data for navigation > & astronomy for the years 1991-1995" from the Royal Greenwich Observatory, > a set of tables that contain the Altitude azimuth data for the sun as a > function of time in polynomial form which is even easier to use for > computation. > Hence I could calculate the direction of the sun for any time > on any date. I have since purchased the tables for 1996 - 2000. In plotting > the annalemas for different years I realized that there shape was year > independent which from our preceding discussion is not at first obvious:-) Yes, except for the slowly changing change in magnitudes of obliquity and eccentricity that Luke refers to. It is so much easier for me, now, to fit the calendar to the analemma rather that the other way around, in a way similar to your use of the weeks on the analemma themselves. The ONLY value to this, methinks, is to show the ability of a sundial to act as a calendar. (I guess that it will also demonstrate the need for Pope Gregory's modification to the Julian Calendar!) < realized as I could draw many designs and pick the one I thought was best > for the size and shape of the wall. I also discovered that the previous > program based on the Ephemeris was in error having corrected for Sidereal > to solar time twice! This led to an error of 4 minutes at the end of the > day:-( In numerical work such as this its nice to have at least two > different ways of calculating something as an error check:-) Oops! (Yes) > Once the size was decided I generated a file of x-y coordinates in inches > from the base of the Gnomon for every minute to generate a smooth curve. You selected the "hour" first then did the minutes around the "hour" for each day of the year to generate a figure-of-eight for that "hour"? Then repeated the process for all of the other "hours"? > Gene Olson then took this into his CAD program an generated the full size > drawings which he used as templates to bend the bar stock to. You can see > a picture of Gene placing them on the wall at: > http://www.concentric.net/~mettlewk/sundial.htm > > Thats probably more detail than most of you wanted. At the risk of being selfish on this list, this is a great "how to" explanation, which I for one, appreciate very much, John. Thank you Tom
Re: Internet Time, GMT, UTC et.c.
Hello Slawomir, Tremendous post. "Slawomir K. Grzechnik" wrote: > In reality time service on the Internet is taken very seriously these days. > Most servers use internally UTC (GMT) and are synchronized through the net > which is not that simple if you take into account variable route and time > of arriving packets. Yet more or less it is done fine thanks to smart IETF > engineers and few protocols they devised. Really important servers are > synchronized by chips receiving time signals. How is the synchronization done to preserve precision and accuracy between stations? There are so many technologies nowadays which are dependent upon consistently accurate and increasingly precise time (GPS, Broadcasting, Space work, etc.) that synchronization among stations is, as you say, not trivial. (UTC time updates at different locales would be dependent upon path lengths and characteristics of the transmission media.) Is signal dispersion an issue? (i.e. difference between phase and group velocity) Are we into relativistic effects when transmitting/receiving between stations with a relative velocity? > Linux (free Unix) calendar program "cal" has range 1- years. It does > include the transition to Gregorian Calendar which in the British Empire > took place in 1752. In Catholic countries the reform was introduced in > 1582, as prescribed by Pope Gregory, and in Oct of that year 11 days were > skipped. There were reports of rioting in many places as people believed > that the Pope robbed them of 11 days of their lifes. 1600 was the first > centurial year that was a leap year in countries that accepted the calendar > reform in 1582. > > This is the output from Linux "cal" for Sep 1752 (Unix was originated on > American soil so 1752 for skipping days is correct) > >September 1752 > Su Mo Tu We Th Fr Sa >1 2 14 15 16 > 17 18 19 20 21 22 23 > 24 25 26 27 28 29 30 I recall reading (somewhere) that the riots were caused by the fact that landlords charged one month of rent for October, 1582 while the tenants got only 20 days of accommodation. I wonder what the money-lenders did! How were dates communicated between Catholic countries and British Empire countries during the period 1582-1752? Thanks again for a most informative and clarifying post. Tom Semadeni Britthome Bounty ><<*> 45.768* North 80.600* West
Re: proposed sundial
Hi Pieter, You might want to check out the dial of one third the magnitude at: http://sciencenorth.on.ca/AboutSN/polaris/index.html If you send me some .jpegs, I could comment on your huge project with more focus. Cheers, Tom Pieter M DeKock wrote: > We are in the process of designing a horisontal sundial for the southern > hemisphere with a gnomon height of over 40m. We would be grateful to receive > any response with regard to any of the following: > > -common errors to avoid during concept, detail drawing and construction > stages; > > -flagging of any issues concerning the size & shape & material of the > gnomon/style; > > -any other information that would help ensure that the practicalities of > designing a sundial on this scale are met. > > Pictures of the proposal are available as jpeg files. > > Pieter.
Re: proposed sundial
Hi Pieter, Thanks for the 4 .jpegs. That is a colossal sculpture! I'm not sure that I understand the function of the variety of "gnomons", spheres, and suspended planar surfaces. It appears quite complex at first sight. Perhaps you could elaborate. The first challenge that springs to mind is the type of shadow that is cast by a slender gnomon upon a plane surface a long ways away. I assume that you will want to use the tip of the gnomon as a seasonal marker in some way. I suggest that you use a dimensioned "pole" cantilevered from a high roof-top to look at the shadow carefully. You will also be able to experiment with the surface colour and texture of the dial face using the shadow of this set-up. You are going to have significant aerodynamic forces due to lift, drag and, interestingly, the shedding of vortices from all of the shapes. The shedding of the vortices off of the struts, cables, and the planar surfaces will cause vibrations which can lead to enormous resonance loads, large enough to destroy the structures. There is no question that you MUST consider aerodynamic loads in this project. At the Science North "Celeste", http://sciencenorth.on.ca/AboutSN/polaris/index.html , I had to decouple the various sections of the semicircles to prevent the thing from shaking itself apart in a 50 km/hr wind. Here is a good URL to look at some of the aerodynamic (q) loads: http://www.lerc.nasa.gov/WWW/IFMD/airplane/short.html I trust that this is a helpful start. Cheers, Tom Pieter M DeKock wrote: > We are in the process of designing a horisontal sundial for the southern > hemisphere with a gnomon height of over 40m. We would be grateful to receive > any response with regard to any of the following: > > -common errors to avoid during concept, detail drawing and construction > stages; > > -flagging of any issues concerning the size & shape & material of the > gnomon/style; > > -any other information that would help ensure that the practicalities of > designing a sundial on this scale are met. > > Pictures of the proposal are available as jpeg files. > > Pieter. -- Tom Semadeni O [EMAIL PROTECTED] o aka I (Ned) Ames . Britthome Bounty ><<*> Box 176 Britt ON P0G 1A0 'Phone 705 383 0195 fax 2920 45.768* North 80.600* West
Re: Heliochronometers: Equation of Time
Hi Pete, Thanks very much for your help in calculating the "average over 4 years-sort of" analemma as shown in your http://netnow.micron.net/~petes/sundial/dialcalc.htm. Luke Coletti also sent me a really helpful table off-list. And I like your Bi-Millennial figures-of-eight, indicating the non-trivial precessional change that Luke mentions. This whole discussion has changed my paradigm to one of fitting the current calendar to the analemma rather than the reverse. I think that I was sucked into the much more artificial reverse by the practice of calculating EoT as a function of calendar dates, rather that as a function of local max (noon) elevation. I guess that it is instructive to remember what the independent variable really is in this case! The dials athttp://netnow.micron.net/~petes/sundialare beauties. Have a look at my big "Sundial" at: http://sciencenorth.on.ca/AboutSN/polaris/index.html Merci, eh. Tom
Swatch/Internet Time/UTC synchronization - again
Hello Dialists, Off the topic of Sundialling -- Resource to earlier discussion re Swatch/Internet Last URL has clever Lewis Carroll, Walt Kelly and other cartoons. Astronomer Andrew Yee's sharp eyes noted this in today's New York Times: http://www.nytimes.com/library/tech/99/03/biztech/articles/07time-review.html) In the event that the article is archived by the time you get to it, Swatch/internet time is described at http://www.swatch.com/internettime/beatnik_fs_time.html and a Time Synchronization Server has Network Time Protocols at http://www.eecis.udel.edu/~ntp/ with an abundance of educational material at http://www.eecis.udel.edu/~ntp/ntp_spool/html/index.htm authoritative but thick. Cheers, t See http://sciencenorth.on.ca/AboutSN/polaris/index.html -- Tom Semadeni O [EMAIL PROTECTED] o aka I (Ned) Ames . Britthome Bounty ><<*> Box 176 Britt ON P0G 1A0 'Phone 705 383 0195 fax 2920 45.768* North 80.600* West
Re: What a great list.
As Jim Cobb would say, oi-may ussi-ay Or as I, a Canadian, would say : Moi aussi, eh? or, bilingually, pas d'sweat! Thank you for such good stuff. t Clem Padin wrote: > Very well put Jim! I think we all agree with you. I too have been > impressed, have learned, have been helped, have laughed!, and have shared > when I could. > > thanks to you all! > Clem > > At 08:41 AM 04/06/1999 -0400, Jim Tallman wrote: > >Hello all, > > > > I never cease to be impressed with the international character and > >intellectual content of this list. I am really glad that I stumbled upon > >it (through visiting Fer deVries sundial page one day). I look forward > >each day to seeing what you guys are talking about, and contribute when I > >can. > > I am a professional product designer, concentrating on things visual and > >aesthetic most of the time, but I am also a perpetual student as well. > >Design is a game of analogies, and the more you know and are exposed to, > >the better the end result will be. While some of my professional > >associates are intimidated by technology, I embrace it and the level of > >understanding it can deliver. I doubt that I would be exposed to the > >mathematical/scientific discourse on this list any other way. > > I am also glad that this list rises above the troubled political times > >we live in, and with the exception of the "Professor Ruby" business, > >everyone here seems to be able to get along just fine. I enjoy the virtual > >company of each and every one of the contributors of this list, and I am > >thankful for the opportunity to be a member. Peace to you all. Jim > >Tallman, FX Studios. > > > > -- Tom Semadeni O [EMAIL PROTECTED] o aka I (Ned) Ames . Britthome Bounty ><<*> Box 176 Britt ON P0G 1A0 'Phone 705 383 0195 fax 2920 45.768* North 80.600* West
[Fwd: [Fwd: Name of sunlight recording device.]]
Hello, Alan Nursall at: http://sciencenorth.on.ca/AboutSN/polaris/index.html provides 3 sources for conventional Campbell-Stokes instruments and a source for an electronic sunshine recorder. t -- Tom Semadeni O [EMAIL PROTECTED] o aka I (Ned) Ames . Britthome Bounty ><<*> Box 176 Britt ON P0G 1A0 'Phone 705 383 0195 fax 2920 45.768* North 80.600* West Received: from mail.sciencenorth.on.ca ([24.139.25.3]) by ns.zeuter.com (8.8.8/8.8.8) with ESMTP id GAA17153 for <[EMAIL PROTECTED]>; Wed, 14 Apr 1999 06:02:42 -0400 (EDT) Message-id: <[EMAIL PROTECTED]> Date: Tue, 13 Apr 1999 16:03:11 -0400 Subject: Re: [Fwd: Name of sunlight recording device.] To: [EMAIL PROTECTED] From: [EMAIL PROTECTED] (Alan Nursall) MIME-Version: 1.0 Content-Type: text/plain X-Mozilla-Status2: Content-Transfer-Encoding: 8bit [EMAIL PROTECTED] writes: >Does anybody know the name the device described below? > >It looks like a glass sphere held in the center of a small equatorial >sundial. The image of the sun focuses to a point at some short >distance away from the surface of the glass sphere. Held in place >at this distance away from the glass and following the curve of >the sphere is a piece of waxpaper against a dark background. >When the sun shines, the waxpaper is scorched. When the sun >is behind the clouds, it is not scorched. The result is a recording of >the >amount of sunshine seen at that location on that day. > >At least this is how it appears to me from a picture I have seen. > >Anybody have a name and possibly a source to buy one? - The device is called a Campbell-Stokes sunshine recorder and any distributor of professional-grade weather instruments will sell them. Try Geneq atwww.geneq.com or Casella atwww.casella.co.uk/mccampbellstokesdata.html or Thies Clima at www.thiesclima.de/sonne.htm Orion has an electronic equivalent at: www.orionelectronics.com/solar.htm .. Alan Nursall Science North 100 Ramsey Lake Rd, Sudbury, Ontario CANADA P3E 5S9 Phone: (705) 522 3701 ext 250 Fax:(705) 522 4954 [EMAIL PROTECTED] http://sciencenorth.on.ca 46.5°N 81°W Eastern Standard Time (UTC-5)
Re: bad people on the list
Mark, there is an individual @zianet.com who posted the following subjects: faux granite dial cycloid polar dial helical gnomon plasma cutter to this list in 1999. Hopefully the individual will help clarify the situation for us this week so that we can get to the source of this destructive assault on a super list that we all respect so much. I regard this as an assault not only on the named victim, but on all of us, including me. Yes it is unfortunate that we have to take the time to root this stuff out. But for the sake of the integrity of the list, methinks it is up to us to do so. Thank you for contributing your expertise to the solution. Cheers, t Mark Gingrich wrote: > Richard Langley wrote: > > > Is this really from Fernando? Doesn't sound like it. Note that the > > posting did not origniate from his usual e-mail address but from Hot > > Mail. Do we have a Fernando imposter? > > Yes, Richard, that rude note is obviously from an imposter. The *real* > Fernando Cabral has always sent his missives from the e-mail address > [EMAIL PROTECTED]; the phony Fernando -- obviously a spineless > troublemaker -- is posting from [EMAIL PROTECTED] > > Forgeries such as this are a rampant problem on the 'Net today, especially > with the rise of "throwaway" e-mail accounts from services like Hotmail.com. > Fortunately, these services have finally begun to supply hints in their > e-mail headers as to the true sources of the messages. > > For example, in the posting from our phony Fernando, one of the e-mail > headers shows the sender's originating IP address: > >X-Originating-Ip: [206.206.120.30] . > > Using the "nslookup" service, this IP address corresponds to the following > server/ISP: > >sc021.zianet.com . > > Now, by invoking Unix's "whois" command, we find that zianet.com is located > in New Mexico, USA: > >Registrant: >ZiaNet, Inc. (ZIANET-DOM) > P.O. Box 8368 > Las Cruces, New Mexico 88006 > USA > > Finally, when I send an e-mail to the sundial list server at > >[EMAIL PROTECTED] > > containing just the following two-line message in the body of the e-mail: > > who sundial > end > > ... I get the current list -- 335 subscribers in all -- of sundial mailing > list participants. And wouldn't you know it? There is just *one* person > on that roster with an e-mail address at zianet.com. > > Yes, I know that this is insufficient evidence to convict in a court of > law, but given that there are only three-hundred-something participants > in this forum from the entire world, what are the odds that we would have > *two* different subscribers to this mailing list from the same small-time > ISP serving the sparsely populated southwest desert region of the USA? > Or is it just far more likely that these two individuals at zianet.com > are actually one and the same? > > My apologies to the good folks on the sundial mailing list for having > to put up with the above off-topic administrivia. But knowing how to > determine an e-mail forgery is, sadly, becoming a necessary skill in > today's e-world. I now consider it a must-have tool in one's "baloney > detection kit." > > ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ > Mark Gingrich [EMAIL PROTECTED] San Leandro, California
Re: "accurate" vs. "precise"
Yo John! Old Timers?! Elderly?.or on old time? or been on the list for a while?or? My distant history tells me this: Precision usually means the number of significant figures used to report a measurement. Accuracy usually means how close your reported measurement is to the "truth". Try this scenario: Let's say that the diameter of a rod is measured, using accurate laser interferometry, to be 0. 50148 cm. You measure the diameter with a micrometer using its vernier scale and report the diameter (A) as 0.5025 cm . You then use a coarse pair of calipers and report its diameter (B) to be 0.5 cm. Measurement A is MORE PRECISE because it implies a preciseness of measurement 1000 times, or 3 orders of magnitude, more precise than Measurement B. But measurement A implies that the "true" value of the diameter is between 0. 50245 and 0.50255 cm while measurement B implies that the "true" value of the diameter is between 0.45 cm and 0.55 cm. So measurement B is MORE ACCURATE since the "true" value lies within the implied limits of the B measurement and outside of the A measurement limits. (There is a systematic error in the A measurement of about 0.001 cm, probably due to a non-zeroed anvil measurement.) Dial accuracy is affected by the accuracy of placement and orientation of all of the components. Dial precision is affected by the clever use of geometry, scaling, and interpolation lines to aid the eye to read the edge or body of a shadow precisely. John Shepherd's beautiful dial at: http://www.uwrf.edu/sundial/welcome.html demonstrates a clever trick to increase the precision of an accurate dial. The trick is shown explicitly at: http://www.uwrf.edu/sundial/images.html where the good Professor shows three close-ups taken sequentially at 9:58, 10:00 and 10:02 am Central Daylight Time. The eye/mind is very good at extrapolating to a point, much better than finding and reporting the edge of a fuzzy shadow! The short and long of it, John, is that you shouldn't use "accurate", "precise" and "old timer" without proper explanation! It seems that there was a discussion on this list a long time ago about tricks to help the eye get increased precision of dial time. There must be some rules of thumb about shadow distance, contrast, color etc. that would help us in our quest for precision (assuming that our dial is free of the normal errors!). I, for one, would appreciate some pointers (pun) on the topic of enhancing precision. Cheers, and congratulations at being at the proofreading stage of your Manual. Good stuff. t Phil Pappas wrote: > Hello Old Timers: > > I've got another knit-picky question for you all to ponder. But you're a > rather knit-picky group, so I don't think you'll mind. > > In proofreading the new fifth edition of my "Sundial Owner's Manual", when > discussing sundials, I think that I mistakenly used the words, "precise" and > "accurate", interchangeably, as if they meant the same thing. > > > John Carmichael > Tucson > tel: 520-696-1709 > website: http://www.azstarnet.com/~pappas -- Tom Semadeni O [EMAIL PROTECTED] o aka I (Ned) Ames . Britthome Bounty ><<*> Box 176 Britt ON P0G 1A0 'Phone 705 383 0195 fax 2920 45.768* North 80.600* West
Re: "accurate" vs. "precise"/ to 01 May
Ok, John here is an accurate report to date: On Thu, 29 Apr 1999 08:35:38 -0700 (MST) John Carmichael Tucson tel: 520-696-1709 website: http://www.azstarnet.com/~pappas corresponding out of: [EMAIL PROTECTED] (Phil Pappas) asked whether the terms "accuracy" and "precision" are interchangeable. --Summary of responses--- There were 32 independent replies from 21 people, up to and including Malcolm Purves <[EMAIL PROTECTED]> Sat, 01 May 1999 11:39:07 +0100) The following can be concluded: This list is populated by creatively independent folk who tend to be happily diverted into precise minutiae well wide of the famed moving shadow. The accuracy of this statement can be correlated to the measurement of the pH of the fluid in our moderator's stomach as he debates "on topic or off topic?". I selected one subject of interest (IMHO) from each of the posters in chronological order to give the following sample: misaligned heliochonometers, Old Timers (ancient sundials?!), relativity, accurate by agreement, Heisenberg's Uncertainty Principle, truth, standard deviation, lice removal, tightly grouped around the bull, Tukey's test, wrong, barleycorns in boots and shoes, stroke of mercy, cost of precise accuracy, the ubiquitous BYA which is a smallish unit of energy, Statistical Treatment of Experimental Data, furlongs and fifths, pfund, Robert Pershing Wadlow, Fernando! and finally, &[EMAIL PROTECTED] Methinks we owe a vote of thanks to our moderator for tolerating this eclectic miscellany (that one is for you, F.C.!) which has an enormous deviation from the meaningful. It even takes a leap of faith to accept that the central tendency has anything to do with the moving shadow. I have a nagging question, though. If I measure the time of the summer solstice in 1999 how do I use the words "accurate" and "precise" or their derivatives in describing my measurement of the instant of this event? Lice, you say, John? Only down under? Pity. BTW how WOULD you make the above measurement? Thanks, t -- Tom Semadeni O [EMAIL PROTECTED] o aka I (Ned) Ames . Britthome Bounty ><<*> Box 176 Britt ON P0G 1A0 'Phone 705 383 0195 fax 2920 45.768* North 80.600* West
Re: (Off topic) Left or Right?
Mike, It would be fair to tell us which week, so that tourists would know when to avoid the "aulde countrie" when scheduling visits. Somehow I've lost the connection to the moving shadow edge. Except for... The only vehicular direction that seems to relate to the edge of the moving shadow is "traffic flow" around a roundabout. In those countries where the steering wheel is on the sinister side folks would round around the roundabout in a clockwise or dialwise direction. I.e., the left hand rule applies so that the thumb is up! On the other hand, right side steering wheeled carriages usually turn counterdialwise or antidialwise around the roundabout and the right hand rule rules. As in Britannia. I think that I have the hands, rotations and rules right, right? Knighty Knight, t The Shaws wrote: > We (UK) keep to the left side of the road, so that our > (normally) strongest hand is available to fight an enemy > with a sword - a throwback to the days of King Arthur and > his Knights I suppose. > > There was a rumour going round that the governmment were > considering changing us to driving on the right - but they > would introduce the system gradually: > > Bicycles and motorbikes would change on Monday > Cars would change on Wednesday > Lorries and Buses on Friday > > Mike Shaw > > [EMAIL PROTECTED] > 53.37N 3.02W -- Tom Semadeni O [EMAIL PROTECTED] o aka I (Ned) Ames . Britthome Bounty ><<*> Box 176 Britt ON P0G 1A0 'Phone 705 383 0195 fax 2920 45.768* North 80.600* West
Re: update on Schmoyer sundial/Sufficient Precision
Reference: R. Bailey's last sentence below: Hooray! At last! An operational definition for "Sufficient Precision"! Proposed by "an engineer, of course." (For those of you unfamiliar with the traditional relationship between Canadian engineering students and Lady Godiva it was "...an engineer, of course, who noticed that Godiva rode a horse.") Observant chap, Roger, probably also observes the rotation of Earth by watching "The Walking Shadow". Roger Bailey wrote: > Hi Jim, > > I own an Aquitaine Dial by Morrison Associates, the Bacchus version > decorated with grapes and vines. It was a gift from someone who knew of my > passions well. I am impressed with the artistry and construction. > Morrison's associates are well known in this community of dialists as > recognized experts in the history and design of sundials. I have seen > other Morrison dials in shops and can recommend that they provide value for > the price. > > The historical lore included in the package and displayed on the web page > adds to the appeal of the Aquitaine dial. It is not as accurate or > universal as the Explorer version (a folding equatorial) but it is > sufficient precise for arranging trysts. > > Roger Bailey > Walking Shadow Designs > N 51 W 115 > > -- Tom Semadeni O [EMAIL PROTECTED] o aka I (Ned) Ames . Britthome Bounty ><<*> Box 176 Britt ON P0G 1A0 'Phone 705 383 0195 fax 2920 45.768* North 80.600* West
International registration of Sundials
Hello, Following Peter's excellent idea: It seems sensible to develop an international registration system which: 1)Assigns a unique identifier to each dial, with priority given to publicly accessible dials. 2)Stores identifiers and pics of each dial in some sort of web accessible searchable file. 3)Encourages owners and organizations to display the identifier and any other theft-deterrent information at the dial site, or on the dial itself if advisable. To achieve two purposes: 1)Broaden public appreciation of the dialist's art, science and craft over the years. 2)Enhance the security of dials, especially publicly accessible ones. Maybe a discussion on this list looking at purposes, feasibility, system attributes and development and maintenance would be helpful. Tom Peter Tandy wrote: > Patrick Powers has a point here, but on balance I think fernando (with a > small 'f' !) has a stronger point. If we can't ever enjoy these things, > then there really is no point in having them. > Surely we > should be taking the war to them and showing them that there is no hiding > place, across the world, and that eventually a stolen dial WILL be traced. > Perhaps we should start to fix 'official' (that is BSS in UK, NASS in > N.America, etc) stainless-steel plates to dial pillars, walls etc stating > that the dial is fully logged and known the world over, as a deterrent.
Re: plotting timelines for giant sundials
Hi John, Here is a try: John Carmichael wrote: << Snip >> > THE PROBLEM: The plotting techniques which use tabulated angles or > computation produce timeline plotting angles in degrees which the dialist > must mark onto the dial plate using a protractor. These angles will be as > precise as the number of decimal places used in the calculations. However, > even though one takes great care to obtain precise timeline angles, this > amount of precision is useless if one's protractor isn't equally precise. > The graphical plotting method also requires an accurate protractor, of course. <> I assume that you are at the "Layout Stage" here and want to precisely locate the hour and other marks on the actual surface of the Dial. For "Celeste" at: http://sciencenorth.on.ca/AboutSN/polaris/index.html the radius of the dial circle is 20/pi meters, about 6.366 m (just under 21 feet). When laying out the marks I found it easiest to measure the length along the arc of the circle from the reference at north to the various marks, using a flexible cloth surveyor's tape. The center of each brass 15 minute marker is positioned to within .5 mm of where it "should be". There was some "slop" in the positioning when we placed the terrazzo matrix into the welded brass framework which holds the Roman numerals and the quarter-hour marks. I calculated the angles between each of the hour and quarter-hour marks and North. The length of the arc along the circumference of the dial for each angle is given by: arc length = (radius) x (angle in radians), the units being the ones to measure radius. or arc length=(radius)x(angle in degrees)x(pi/180) In the case of Celeste: The dial circle has a circumference, C, of 40 meters. (Another subject, but the reason for this is that both Celeste and Terra are at one millionth scale of Earth, and use the classical definition of the metre, namely, 1/10,000,000 of the distance between a pole and the equator.) Celeste's circumference of dial circle, C = 40 meters Radius, R, of dial circle = C / 2pi Celeste's Radius, R = 40 / 2pi meters = 20/pi meters L, length of Celeste's arc = (20/pi) x (pi/180) = 1/9 meters/degree ~ .1 meters/degree This is 111.1 mm or about 4.37 inches of arc length per degree of subtending angle. You can easily mark to the nearest millimeter, so you can easily mark to the nearest hundredth of a degree. In fact you can probably get down to a half a minute of angle in precision of marking. You can probably guess why I used a pipe for a 20 foot gnomon. (Yes, it is much easier for the eye to interpolate to the centre of two fuzzy shadow edges to make a reading then to debate where the actual shadow is on one side. The symmetry avoids all of the penumbral and diffraction difficulties.The error due to non-linearity of the dial scale is negligible. Besides I needed some rigidity.) Commentary on A, B and C: > SOLUTION A: << Snip >> > I'm thinking that during the construction phase of a very > large sundial, I could make a temporary giant protractor located just > outside the hourline radius. This would be a fairly simple thing to do using > plane geometry. It would be easier to turn your angles using a theodolite at the centre of the dial than to make a giant protractor. I used one to check the time marks before the terrazzo was poured and the hairline was on the brass in every case. Just remember to set the theodolite lower than usual, because you'll have to tilt the 'scope down to mark your angles. And you'll need a helper to hold the pencil point on the marks. > SOLUTION B: If the unit square method is used (Waugh, pg. 40-43), then no > protractor is needed. One only needs a good long measuring tape for laying > out the lines. ( The limits of precision would again depend on the number of > decimal places used.) I don't have Waugh's book. I assume he converts to rectangular coordinates to do the layout. Great solution if you have to transcribe curved or non-radial lines, but a lot of work at the layout stage. Your computer program can usually give you your x-y coordinates as a matter of course - just punch in points on the curves and note the coordinates off of the cursor coordinates. Sometimes it is easier to grid it as finely as you need and then interpolate to give you plot points. > SOLUTION C: What if I built the gnomon first and use its shadow to tell me > the position of the time lines << Snip >> Guess who put up a temporary gnomon for a few sunny days before placing terrazzo! It worked superbly. I wouldn't build a big one without doing some "field checking"! Saves lot of potential embarrassment too. Big dials usually have a lot of volunteer (field supervisors) because they are usually very visible in a public place and these folk can usually be conscripted to hold cardboard and pinholes to sharpen the moving shadow and to call "mark" when the second hand sweeps through 12 on the electromechanical time manufacturer
HELP for Down Under Pilots
John, Really! Aussies are well dispersed in all spatial dimensions, it seems. Scattered lot? In Canada the 2-4 Law is as the Down Under version, but the "directly" is replaced by "inversely". We also have a fudge factor or cooks' constant which is a complex function of proximity of toilet facilities and lengths of queues emanating therefrom. The tendency of the Canadian version of the 2 - 4 Law is to keep us in a bit of a huddle whilst in the wilderness. I'm chuckling too, because I think that you've just been suckered in again. Thank goodness we are in the Commonwealth, or should I wait for a boomerang? Beautiful vernal sunshine here today approaching the stice, good for calibrating sundials. (There, that makes this message legitimate!) Cheers, t John Pickard wrote: > Bill, > > BRILLIANT!!! > > You really suckered me in with that one. > > You are of course aware of the 2 - 4 Law which governs the > distribution of people in the wild?? > > The number of people encountered in the wild is directly proportional > to the square of the horizontal distance from the carpark, and the > fourth power of the vertical distance above or below said carpark! > > Thanks for giving me a really good laugh! > > John > > Dr John Pickard > Senior Lecturer, Environmental Planning > Graduate School of the Environment > Macquarie University, NSW 2109 Australia > Phone + 61 2 9850 7981 (work) > + 61 2 9482 8647 (home) > Fax + 61 2 9850 7972 (work) -- Tom Semadeni O [EMAIL PROTECTED] o aka I (Ned) Ames . Britthome Bounty ><<*> Box 176 Britt ON P0G 1A0 'Phone 705 383 0195 fax 2920 45.768* North 80.600* West
Re: frame & grid method
-- Tom Semadeni O [EMAIL PROTECTED] o aka I (Ned) Ames . Britthome Bounty ><<*> Box 176 Britt ON P0G 1A0 'Phone 705 383 0195 fax 2920 45.768* North 80.600* West
Re: frame & grid method
posite > >>corners. > >> > >>The only problem then is to precisely draw your frame, with parallel sides > >>and a good perpendicularity. > >> > >>With one intersection point you can draw the line by joining it to the > >>gnomon foot. > >> > >>I plan to include such kind of data in my Shadows program in a futur > >>version. > > > >Bonjour Francois and everyone else: > > > >Your frame method for plotting would be a good practical way to implement > >John Pickard's (x,y) coordinate method. With a squared frame around the > >sundial work area, one could use it as a reference to easily measure the > >horizontal and vertical distances to the x,y coordinates. > > > >Let us know when you get your new shadows program up and running. Do you > >think I'd understand it or would I have to get someone to help me? > > > >merci Francois, > > > >John Carmichael > > > > -- Tom Semadeni O [EMAIL PROTECTED] o aka I (Ned) Ames . Britthome Bounty ><<*> Box 176 Britt ON P0G 1A0 'Phone 705 383 0195 fax 2920 45.768* North 80.600* West
Re: Fw: frame & grid method
t; > > If the roots of x are imaginary (i.e. the radical is negative) then > > there is no intersection. > > > > Adjust coordinates of intersecting circle relative to base circle. > > > > I have this function coded in C, QBASIC and assembler if anyone wants it. > > > > Best regards, > > > > Jim > > > > James E. Morrison > > Astrolabe web pages at: http://myhouse.com/mc/planet/astrodir/astrolab.htm -- Tom Semadeni O [EMAIL PROTECTED] o aka I (Ned) Ames . Britthome Bounty ><<*> Box 176 Britt ON P0G 1A0 'Phone 705 383 0195 fax 2920 45.768* North 80.600* West
Re: A dial by any other name
Tony, Many thanks for the wonderful .JPEGs of the "master meridian layout alidade", your conversion of "the 'machinegun fire director' from the Vickers gun - a magnificent Canadian bronze instrument" to peaceful purposes. As to your request for terminology: The "rest of" Canada calls the instrument which measures the instantaneous angular location of Earth as it spins about its axis by measuring the angle of the moving shadow cast by the gnomon (and the style, substyle, and variants thereof) in the sunlight a "sundial". Our fellow Canadians in Quebec have a Special Vocabulary, with special keyboards and laws to transmit and protect it so I'd defer the question to someone in an Official Capacity to inform you and the List of the proper term for what are colloquially known as "Cadrans Solaires". Merci. By the way, in Canada we usually spell it "spelled", eh? Cheers, t Tony Moss wrote: > Fellow Shadow Watchers, >As ever, I turn to The List with a problem. I > need to know the correct term for a sundial in as many languages as > possible but to ensure that I get it right, particularly the spelling!! > :-) could I please ask for contributions - although limited to western > style characters for no other reason than my wordprocessor can only > handle such. > > In return for this kindness I'll publish the resulting list on The List > in case it may be of use to others. > > Thanks in anticipation > > Tony Moss Tom Semadeni O [EMAIL PROTECTED] o aka I (Ned) Ames °. ¿ Britthome Bounty ><<*> Box 176 Britt ON P0G 1A0 'Phone 705 383 0195 fax 2920 45.768° North 80.600° West ° s courtesy W.M.
Re: sundial bracelet
Which reminds me of Alexander's affliction: Lack of a second hand so he couldn't take Aristotle's minutes. *Groan* Sol Invictus: "Traditionally tonight is a time of delightful frivolity." Greg Lambertson wrote: > This reminds me of Aristotle's experiments with wine-soaked cloth, which > gradually changes color when exposed to sunlight. He tied such cloth to his > student Alexander's wrist, for use in determining the passage of time. It > became known as Alexander's Rag Time-Band. ;-)
Re: Another Kipling Heliograph Poem
Thank you, Prof. Langley, for illuminating yet another marvelous facet of this List. Kipling, the author of the ritual for the calling of a Canadian engineer, was a clever dude, eh? Tom
Re: Signalling mirrors
"At least you weren't sending advice a la Kipling's Jones on 'the Hurrum Hills above the Afghan border'," reflected Tom Semadeni.
A Modest Proposal
Dear fellow dialists, According to: http://news.bbc.co.uk/low/english/sci/tech/newsid_38/380035.stm ..."France is to mark out "Le Meridien" with trees and olive groves and a mass picnic, joining the 337 towns and villages over a distance of 960 kilometres."... "In what might be regarded as a piece of one-upmanship, the long line of trees to be planted across France will ensure the Gaelic meridian is visible from space." ... A MODEST PROPOSAL: Traditionalists loyal to the Greenwich Meridian may wish to promote the planting of flora along 24 meridians, the (Greenwich) Prime and the 23 others, which, at least theoretically, center Earth's time zones. What a project! The regreening of the globe along traditional lines. Those who disagree with these Greenwich Longitudes can plant along the parallels of Latitude! We need to get consensus on which lines to plant, though. Why not start with parallels every 5°, an unambitious 300 nm separation, and increase the density to 1° over the years of the new millennium? A serendipitous convergence of GPS technology and B. Fuller's image of Spaceship Earth yielding a reconditioning of Earth's living environment! Yours, with shovel and bucket at the ready, t -- Tom Semadeni O [EMAIL PROTECTED] o aka I (Ned) Ames °. ¿ Britthome Bounty ><<*> Box 176 Britt ON P0G 1A0 'Phone 705 383 0195 fax 2920 45.768° North 80.600° West
