Re: large sundial
Large sundials do have the potential of being more accurate. Essentially a sundial measures an angle and that angle is related to the time. When measuring an angle one achieves more accuracy with a larger angle scale. The problem is that a shadow cast by a central gnomon is not a very good device for precise reading of the scale, this due in great part to the finite width of the sun. If the angle is read by other means the precision may be increased. One technique is to use a swinging device that is positioned using the dissapearance of its shadow. That device can extend out to the outer limits of the dial with the scale that is to be read. I believe that if the swinging device is, for example, a fin with some thickness to it, that it is possible to find that position where it is in line with the sun with a high degree of accuracy, with a higher precision than using a central gnomon. The end of the fin can have a pointer which is used to read the angle. Daniel Wenger Daniel Lee Wenger Santa Cruz, CA [EMAIL PROTECTED] http://wengersundial.com http://wengersundial.com/wengerfamily
Re: BSS Bulletin. Southern Hemisphere Sundial?
x-rich Well spotted! My guess would be horizontal, southern hemisphere. If vertical south-facing the Roman numerals would be upside down seen from below. John Lynes This touches on a question that I have pondered a bit. Perhaps the sundial group can help with the answer. My dial, a globe represention of the earth, when made for a location in the southern hemishpere, has the south pole of the globe pointed towards the south pole. The north pole is below the horizon. The numbers on the analemmas would progress from morning to night along the two tropic lines. My question is: what should the orientation of the numbers be. Is up for those in the southern hemisphere still towards the north pole? This may simply be a matter of taste, but perhaps there is a tradition in southern hemisphere dials about the orientation. Thanks for comment. Daniel Wenger Daniel Lee Wenger Santa Cruz, CA [EMAIL PROTECTED] http://wengersundial.com http://wengersundial.com/wengerfamily /x-rich
Re: Armillary Spheres in Portugal
Roger Thank you for this picture of Portugal and some of the history of navigation. This was new to me. You may want to take a look at my armillary sphere that I made to find the comet Kohoutec. It led to my finding the design of my sundial. http://www.wengersundial.com/uniglobe/index.html http://www.wengersundial.com/uniglobe/globe1.html Regards, Daniel This year my escape from winter in Canada was a trip to Portugal. This offered warm sunshine, scenic sea coast, and an opportunity to stay in the castles and palaces of bygone times. Like many of you, when I travel, I search for sundials. This provides a focus for exploration and often provides a unique window on the people, culture, architecture and history. The search for sundials forces an attention to detail that often brings unexpected rewards. Daniel Lee Wenger Santa Cruz, CA [EMAIL PROTECTED] http://wengersundial.com http://wengersundial.com/wengerfamily
Re: no mail ? Is it normal ?
Actually it is dark, but the lights are on. See the amazing photo at http://antwrp.gsfc.nasa.gov/apod/image/0011/earthlights_dmsp_big.jpg Daniel Wenger I think it has just been quiet. Perhaps there's no Sun in most of the northern hemisphere, and it's just depressing? Dave On Fri, 26 Jan 2001, -ce- wrote: Help ! Am I casted away ? Has the sundial list a problem ? I didnt received any other messages, only those from Tony Moss (thanks Tony !) since the one named : telling time by rainbows, from Frans W. MAES on 15/01/01 at 14:23. Is the activity on sundialling halted all over the world ? I hope it is not the case ! Even if I'm only a reader of tese very interresting exchanges, it gives me many pleasure and knowledge. Gnomonically yours ! Alain MORY 7E 48N Daniel Lee Wenger Santa Cruz, CA [EMAIL PROTECTED] http://wengersundial.com http://wengersundial.com/wengerfamily
Re: Analemma Stuff
Luke Your statement that eccentricity will always be synchonous to the passage of perihelion needs, I believe, amplification. There is no a priori reason that I know of that the mean sun and the actual sun should have the same right ascension at perihelion. The fact is that one may choose the mean sun to have the same right ascension as the sun at any time of the year. The resulting EoT of course will be different and will not average out to zero during the year. There is a point in the year such that, if the mean sun corresponds to the right ascension of the sun, the EoT will average out to zero. It just happens that this occurs very near to perihelion. My calculations show that the position is within a fraction of a degree of perihelion but is not at perihelion. There may be an argument that it should be at perihelion but I do not know that argument. The calculation that I did to find that point where the average EoT goes to zero may be round off error dependant. Can you find my error in thinking or can we agree.? Dan Wenger Hi Bill, If you mean to ask why the EoT was made to be zero at a given set of dates, I think the answer is that it wasn't. One can't arbitrarily make the EoT zero points (four of) synchronous to a set of dates. The EoT has two components, obliquity (the tilt of our axis relative to the plane of our orbit) and eccentricity (the elliptical shape of our orbit). Obliquity will always be synchronous to the four cardinal positions of the orbit (the equinoxes and solstices), eccentricity will always be synchronous to the passage of perihelion. The two components however are NOT synchronous to one another, I have explained this in some detail in earlier messages. In short, because the two components are not synchronous to one another the EoT undergoes variation in time. So a set of 17th century values will definitely not be the same as those today, i.e., the shape of the analemma will be different. Regards, Luke Coletti [EMAIL PROTECTED] wrote: 4/3/00 Does anyone know why the equation of time is indexed to zero on 9/1, 12/25, etc.? That is to say, when the clock was originally being indexed to the sun (17th century?), why did they pick this set of dates as the zero point? Why not, for example, set the clock to where the analemma crosses itself, or to one of the solstices, or equinoxes? I'm sure there is a good reason, but I haven't been able to think of it. Maybe it has to do with indexing the clock to sidereal time, and not to sun time. Any takers? Bill Gottesman Burlington, VT Daniel Lee Wenger Santa Cruz, CA [EMAIL PROTECTED] http://wengersundial.com http://wengersundial.com/wengerfamily
Re: Analemma Stuff
Bill I think that it was not a choice to index to those dates but instead to place the analemma such that the number of days that the EoT is positive is the same as the number of days that the EoT is negative. If the analemma is displaced this balance cannot occur. I discuss this average on my page at http://www.wengersundial.com/math/analemmaCalc.html Dan Wenger 4/3/00 Does anyone know why the equation of time is indexed to zero on 9/1, 12/25, etc.? That is to say, when the clock was originally being indexed to the sun (17th century?), why did they pick this set of dates as the zero point? Why not, for example, set the clock to where the analemma crosses itself, or to one of the solstices, or equinoxes? I'm sure there is a good reason, but I haven't been able to think of it. Maybe it has to do with indexing the clock to sidereal time, and not to sun time. Any takers? Bill Gottesman Burlington, VT Daniel Lee Wenger Santa Cruz, CA [EMAIL PROTECTED] http://wengersundial.com http://wengersundial.com/wengerfamily
Re: equation of time
Willy Simply put, the actual sun moves irregularly in the ecliptic plane, the mean sun may be thought to move uniformally in the earth's equatorial plane. In the first the ellipse is involved, in the second the obliquity of the earth's axis is involved. Dan Wenger The equation of time has two causes. The first is that the orbit of the earth around the sun is an ellipse and not a circle. The second is that the plane of the earth's equator is inclined tot the plane of the earth's orbit. Please can anyone explain me the second cause so that I can conceive it. I am not a astronomer! You can do it in Dutch (for preference), in French, in German or in English. Willy Leenders Hasselt Belgium Daniel Lee Wenger Santa Cruz, CA [EMAIL PROTECTED] http://wengersundial.com http://wengersundial.com/wengerfamily
Re:
Alain and dialists You will find at http://www.wengersundial.com/Cylinder/Cylinder.html information on the cylindrical tower sundial. The problem is an interesting one with an interesting solution. I can provide more detail if desired along with the data values that could be used to place the analemmas on the tower. The analemmas were computed for 47°N 7°E which I assume is the location of the tower. The other parameter used was the ratio f=r/R where r is the distance of the gnomon to the tower wall and R is the radius of the tower. The values used in the calculation were .2, .4 and .6. The gnomon was assumed placed due south. This need not be the case. Enjoy. Dan Wenger Daniel Lee Wenger Santa Cruz, CA [EMAIL PROTECTED] http://wengersundial.com http://wengersundial.com/wengerfamily
EoT and declination of the sun
Dear Dialists A few days ago I posted email regarding the desirability of regarding the analemma as a function of the sun's declination and attempted to point out that the traditional exposition of the EoT by relating it to the date was causing confusion about the stability of the analemma. Communications with Arthur Carlson and Luke Coletti have added to my understanding of the issues and further study of my program to calculate the EoT versus the sun's declination has enlightened me further. In my original program I mentioned that there was an implied assumption that at perigee/perihelion the right ascension of the mean sun was identical to the right ascension of the sun. This is patently incorrect and I would have found my error simply by looking at the data that the program generated. What I should have said was that there was an assumption that at perigee/perihelion the right ascension of the mean sun is numerically equal to the ecliptic longitude of the sun at perigee/perihelion. This assumption was used in the calculation that produced the data. It became to clear to me that this was a critical assumption and I needed to determine the basis for that assumption. In looking more closely at the notion of a mean sun one is led to a mean sun that is as close to the right ascension of the sun as possible during the year. This led me to look at the sum of EoT for each time of calculation over the year. One measure of closeness to the sun is that the sum of EoT over the year be zero. By varying the assigned right ascension of the mean sun at perigee/perihelion I was able to determine a value that gave a sum of EoT of zero. That numerical value differs from the ecliptic longitude of the sun at perigee/perihelion by 0.00039735 degrees It is a bit of a mystery as to why this should be the case. I have added this term to my analemma calculation at http://www.wengersundial.com/Analemma/analemmaCalc.html and have generated new data at http://www.wengersundial.com/Analemma/analemmaData.html The new data differs from the original data by at most a second in the value of the EoT. The calculated extremes do not change. Life truely is beautiful. Dan Wenger Daniel Lee Wenger Santa Cruz, CA [EMAIL PROTECTED] http://wengersundial.com http://wengersundial.com/wengerfamily
Re: Declination Table
Art At the solstices there is no ambiguity. The analemma intersects the tropic of cancer and the tropic of capricorn at one point so there is only one value for the EoT. At all other times of the year, except for one instant when the two paths of the analemma cross, there is only the need to know which leg of the analemma to use. This does not require knowledge of the date, only knowledge of the season. True, the date of the solstices is needed if one is to know if the sun has started north or south yet. In the spring the lower right leg is used (with the analemma viewed projected onto a sphere with the gnomon in front of the analemma, upper left if the analemma is projected onto a surface behind the gnomon), upper left in early summer, upper right in late summer and lower left in the fall. I place a small arrow on each leg of the analemma to indicate the motion of the sun during the year. This identifies to the user which leg to use. One could also label each leg with the season but there does not seem to be reason to know the date. I have attached two views of the analemma, one as projected onto a sphere and one projected onto a plane behind the gnomon. The first shows the arrows that I use, the second I have labeled with the season. Dan Wenger Daniel Lee Wenger [EMAIL PROTECTED] writes: The reading of standard time via a sundial may be accomplisted by mearly reading the declination of the sun and using an analemma, determining standard time. At no point is the current date needed to do this. Way, way back I explained why I was not totally satisfied with this method, essentially because there are (almost always) two values of the EoT for each value of declination. At the solstices there are even an infinite number of values (in some technical sense). Consequently, if you are interested in relating the sundial reading to clock time, you always need some knowledge of the current date. Art Carlson Attachment converted: Macintosh HD:analemma.arrows.gif (GIFf/GKON) (FB7A) Attachment converted: Macintosh HD:analemma.labeled.gif (GIFf/GKON) (FB7B) Daniel Lee Wenger Santa Cruz, CA [EMAIL PROTECTED] http://wengersundial.com http://wengersundial.com/wengerfamily
Re: Design challenge
John My recent postings relate to this question. The leap year is not relavent in the use of an analemma for reading standard time. The leap year is an adjustment to keep the number of rotations of the earth in synch with the revolution about the sun. The reading of standard time using an analemma should make use of the declination of the sun and that is completely independant of issues relating to the rotation of the earth. The difference in right ascension of the sun and of the mean sun (the EoT) is independant of the rotation of the earth on its axis and is only dependant upon the revolution of the earth about the sun. The EoT has meaning if there were no rotation of the earth or an arbitary rate of rotation for the earth. The mean sun is a construct that can be defined completely independantly of the rotation of the earth. Once the mean sun has been defined it may be used to measure the rate of rotation of the earth and of the position of Greenich meridian as a function of the mean sun time. I would suggest that a spherical dial is the most accurate as the reading of the time is as accurate at noon as at any other hour of the day. If the Singleton dial uses an analemma based upon a mean EoT then it is date related and not declination related. Per my arguments this analemma is not correctly designed to be accurate and invarient over a period of years. If the mean EoT is the same as the declination related analemma then the word mean can be removed and it will be accurate over a period of years. Dan Wenger Hi all, I have a question/challenge to all you sundial designers: what is the most accurate design for a Standard Time dial? The reason behind the question is to find a way to stop members of the public looking at a public dial, inspecting their watches, and concluding that dials never tell the right time! The criteria for the dial are, in my opinion: a) it should tell Standard Time, (or possibly Daylight Saving Time - BST in the UK) b) it should be in a fixed location c) it must have no moving parts (which rules out adjustable equatorials and changeable gnomons etc) and should be as physically robust as possible. d) it must not require reference to a separate table or computer program eg to get an exact declination for the sun. All data must be built into the dial plate. e) the accuracy should be interpreted as the mean error for the hour lines 3 hours either side of noon (or 12:00) for the years 2000 to 2050. As a starter, the Singleton dial recently discussed here would seem to be a reasonable candidate. It's main limitation, common to all dials which incorporate an EoT correction, is that it is drawn for a some MEAN EoT curve, and no allowance is made for the leap year cycle and the other minor variations. Is there some geometry of dial plate and style which minimises the time error caused by small year-to-year variations in the mean daily declination? If this is achieved, then the small change in the EoT over a single day may be allowed for. There is no prize for the competition, but I promise I will build a physical example of the best suggestion, and share it with the list! Happy designing, John -- Dr J R Davis Flowton, UK 52.08N, 1.043E email: [EMAIL PROTECTED] Daniel Lee Wenger Santa Cruz, CA [EMAIL PROTECTED] http://wengersundial.com http://wengersundial.com/wengerfamily
More analemma calculations
Dear Dialists I have augmented the information posted a few days ago regarding the calculation of the analemma. There is now also a program that computes the analemma for every hour and projects the analemmas onto a user defined plane surface of arbitrary orientation, ie. horizonal, vertical, equatorial, vertical facing 10 degrees west of south, etc.. I believe that there have been some postings in the recent past asking for details on the calculation of the analemma for a dial designed for a vertical wall facing in some direction. This program handles that need. On this page are gif files showing the projections for various configurations of interest. http://www.wengersundial.com/Analemma/analemmaDetails.html Dan Wenger PS Fixed some notational problems in the original program. Program has not changed. Daniel Lee Wenger Santa Cruz, CA [EMAIL PROTECTED] http://wengersundial.com http://wengersundial.com/wengerfamily
Re: Declination Table
Dear Dialists In my humble opinion I think that discussions of exact dates when certain events happen is not really relavent to the design of a sundial. If one is interested in a dial measuring standard clock time then one is interested in the analemma. But the analemma is a relationship between the difference between sun and mean sun time and the sun's declination. This is unchanging as far as sundial design goes, ie. over periods of time where the obliquity may be considered constant, the vernal equinox constant, etc. Problems arise when one attempts to put a date (and time) to the solstices, equinoxes, etc. These events are changing yearly due to the fact that the year is not a multiple of the daily rotation of the earth. But these changes are not relevant when one attempts to design a sundial showing standard time. The reading of standard time via a sundial may be accomplisted by mearly reading the declination of the sun and using an analemma, determining standard time. At no point is the current date needed to do this. This is not to discourage the analysis of the dates when solar events happen. This is a truly interesting subject, but it does not bear on sundial design in my opinion. If one wants a sundial to show the dates that events happen, then there needs to be additional information supplied to the dial beyond what the sun can tell the user. Ie., one cannot determine the date of a solar event such as the equinox from information derived from the sun. One can of course determine when the equinox happens, ie., right now, or sometime between yesterday and today, etc. but without looking at a calender the date of that event cannot be determined by the sun via a sundial. Hope that this is helpful and can generate some discussion and consensus on the subject. Dan Wenger Daniel Lee Wenger Santa Cruz, CA [EMAIL PROTECTED] http://wengersundial.com http://wengersundial.com/wengerfamily
Re: Azimuthal sundials - again
I should point out that my dial reads time by a projection of a point onto a point (the first point being on a surface) and that it reads standard time. Dan Wenger Gianni wrote: The Monofilar and Bifilar sundials can be built with any kind of Time: Middle Time (Standard), Local Apparent Time, with Italic, Babylonian, Temporary hours, etc. Ah ha! I must have misunderstood the issue being discussed. I can see that in abstract terms that we have dials which are - projection of a point onto a surface (perhaps curved) - projection of a line (perhaps curved) onto a surface (perhaps curved) - projection of two lines (perhaps curved) onto a surface (perhaps curved) - other non-projection types, such as the wonderful CD-diffraction dial. If the third class is already known by common usage as Bifilar, then I accept that it makes sense to call the second type Monofilar (even though for me personally the word filar carries an implication of a wire or thread, rather than being a general term for a line or edge). I assume the first class are called Nodal. The other half of the discussion is what to call a dial with a seasonal time adjustment. I though that someone was suggesting that because the existing examples had already been called monofilar then that name applied to the adjustment feature. So a monofilar dial can be Standard, Local , or other hours Upright, polar axial (axial?), or other principal axis Horizontal, Vertical or other dial face planes So the ordinary garden dial could be called Axial Local Horizontal Monofilar, Mr.Singleton's dial is Axial Standard Horizontal Monofilar. The various forms af azimuthal dials are all Upright monofilars. The Wenger dial is a Local Spherical Nodal dial. Am I getting close? Steve Daniel Lee Wenger Santa Cruz, CA [EMAIL PROTECTED] http://wengersundial.com http://wengersundial.com/wengerfamily
Re: Univeral dial
The notion of a Univeral dial is interesting. My Wenger Sundial has some of the elements of such a dial. Currently the sphere that I use to represent the earth has a hole in it at the base for introduction of the center piece that is used to establish the subsolor point and thus to determine the time. Conceptually the sphere can be made without the hole and with the center piece introduced in some other way. Then the sphere may be rotated and placed with the users position in the local zenith and the poles aligned and the dial is set for reading the time anywhere on the surface of the earth. BUT, the numbering of the analemmas is time zone dependant. Just leaving off the numbering of the time zones is still not going to do the job since time zones do not always match up with the 15 degree longitude lines. There are zones that use the 7 1/2 + 15 degree longitude lines. Also, although my dial does show standard time and daylight saving time when used, not all countries use daylight saving time, ie. Japan for example. So, even though my design has some of the features of a Universal dial, namely it reads mean time and has the same accuracy no matter where used on the earth, ie. good at all latitudes, it still does not meet the desired goals of a Universal dial. Just some rambling on the subject. I think Sara's comments re taxonomy are excellent and need to be applied consistently. Dan Wenger I have to agree with Sara Schechner about taxonomy. We really MUST keep to a standard format for describing all dials. I have one question for Sara. In the case of a universal dial, you say, 'a dial adjustable for multiple latitudes'. I feel that we should perhaps sub-divide this into 3 (or possibly more) categories. I look forward to any comments that you may like to make. 1 A dial that covers all latitudes 90°N to 90°S. This is truly UNIVERSAL. (We could even apply this to dials that perhaps do not quite reach the 90° of both poles. Many only cover 80°N-80°S or thereabouts). 2 A dial that covers just the Northern Hemisphere (or Southern). This could be called SEMI UNIVERSAL. But then, should we specify which hemisphere? 3 A dial with a limited range of useful latitudes, like a Butterfield, this could be PART UNIVERSAL. (It doesn't sound nice. There must be a better description.) There are also some dials, quite rare that cover 60°N to 10°S. I think that I would call these PART UNIVERSAL. The question therefore is, 'What can we call these various sub- divisions of UNIVERSAL?' I look forward to your comments. As an alternative approach we could get round this by specifying the angles of universality. e.g., UNIVERSAL 60°N - 10°S. This is a more scientific way of doing it. Again, I look for your comments. Regards, Mike. [EMAIL PROTECTED] Cambridge, UK. Daniel Lee Wenger Santa Cruz, CA [EMAIL PROTECTED] http://wengersundial.com http://wengersundial.com/wengerfamily
Re: Declination Sun and timeequation
To complement this information I have posted a C language program to calculate the sun/mean sun difference in right ascension as a function of the declination. Data from that program is also given. Please see http://www.wengersundial.com/Analemma/analemmaDetails.html Dan Wenger For sundial design purposes I had a table made by the mainframe computer of my employer. This table gives for every day in the year the mean values of the declination and timeequation measured over the coming century: 2000 - 2099. The values are for 12:00 GMT(noon). I used the original formulas from 'Explanatory supplement to the Astronomical Ephemeris' published by HM Stationery Office in London. You can find it on: http://www.chabot.demon.nl/sundials/SunMeanGMT.htm - Thibaud Taudin-Chabot 52°18'19.85 North 04°51'09.45 East home email: [EMAIL PROTECTED] (attachments max. 500kB; for larger attachments contact me first) Daniel Lee Wenger Santa Cruz, CA [EMAIL PROTECTED] http://wengersundial.com http://wengersundial.com/wengerfamily
Re: graphic conversion
Thanks Jeff. I already use this software. It is wonderful. I have found that I get the best results in putting mathematical equations on the web by composing the equations in Word using Equation Editor, printing to a postscript file, converting it to PDF format using Acrobat Distiller and then doing screen dumps to a PICT file which is loaded using Graphicconverter. The image is then trimmed and converted to GIF format from within Graphiconverter. Dan Wenger For graphic conversion, if you use a Macintosh, consider this fine piece of shareware: Graphicconverter http://www.lemkesoft.de/ It reads and writes the following formats. (see below) To do EPS (postscript) you need a third-party utility for which there is a separate charge. It does not do pdf, which I believe is proprietary. It also has the advantage of being available in a great many different languages. Jeff Adkins Import file formats: PICT, Startup-Screen, MacPaint, TIFF (uncompressed, packbits, CCITT3/4 and lzw), RIFF, PICS, 8BIM, 8BPS/PSD, JPEG/JFIF, GIF, PCX/SCR, GEM-IMG/-XIMG, BMP (RLE compressed BMP's also), ICO/ICN, PIC (16 bit), FLI/FLC, TGA, MSP, PIC (PC Paint), SCX (ColoRIX), SHP, WPG, PBM/PGM/PPM, CGM (only binary), SUN , RLE, XBM, PM, IFF/LBM, PAC, Degas, TINY, NeoChrome, PIC (ATARI), SPU/SPC, GEM-Metafile, Animated NeoChrome, Imagic, ImageLab/Print Technic, HP-GL/2, FITS, SGI, DL, XWD, WMF, Scitex-CT, DCX, KONTRON, Lotus-PIC, Dr. Halo, GRP, VFF, Apple IIgs, AMBER, TRS-80, VB HB600, ppat, QDV, CLP, IPLab, SOFTIMAGE, GATAN, CVG, MSX, PNG, ART, RAW, PSION, SIXEL, PCD, ST-X, ALIAS pix, MAG, VITRONIC, EPSF (with the help of EPStoPICT), Meteosat5, Sinclair QL, VPB, j6i, ASCII, ESM, CAM, PORST, Voxel, NIF, TIM, AFP, BLD, GFX, FAX3, SFW, BioRad, PSION 5, KDC (only PPC), QNT, JBI, DICOM, FAXstf, SKETCH, CALS, EletronicImage, X-Face, NASA Raster-Metafile, Acorn Sprite, HSI-BUF, FlashPix (with QuickTime 4), ISS, RLA, VBM, HPI, CEL, WBMP, PGC, PGF. Export file formats: PICT, Startup-Screen, MacPaint, TIFF (uncompressed, packbits and lzw), GIF, PCX, GEM-IMG/-XIMG, BMP, IFF/LBM, TGA, PSD, JPEG/JFIF, HP-GL/2, EPSF, Movie (QuickTime), SUN, PICS, PICT in Resource, PBM/PGM/PPM, SGI, TRS-80, ppat, SOFTIMAGE, PNG, PSION, RAW, WMF, XWD, XBM, XPM, Clip, ASCII, PAC, ICO, RTF, VPB, Finder Icons, PSION 5, X-Face, ISS, CEL, WBMP, PGC. Daniel Lee Wenger wrote: I wonder if anyone in this group knows of software that converts a Word file to a gif or jpeg or a postscript file to a gif or jpeg or a PDF file to a gif or jpeg. Thanks for any help. Dan Wenger Daniel Lee Wenger Santa Cruz, CA [EMAIL PROTECTED] http://wengersundial.com http://wengersundial.com/wengerfamily -- =-=-=-=-=-=-=-=-=-=-=-=-= [EMAIL PROTECTED] Jeff Adkins Location: 38.00 N, 121.81 W CA, USA, Earth, Sol III Daniel Lee Wenger Santa Cruz, CA [EMAIL PROTECTED] http://wengersundial.com http://wengersundial.com/wengerfamily
graphic conversion
I wonder if anyone in this group knows of software that converts a Word file to a gif or jpeg or a postscript file to a gif or jpeg or a PDF file to a gif or jpeg. Thanks for any help. Dan Wenger Daniel Lee Wenger Santa Cruz, CA [EMAIL PROTECTED] http://wengersundial.com http://wengersundial.com/wengerfamily
Re: patents copyrights
Some thoughts on patents. 1) Is the design patentable? Note that there are mechanical patents and design patents. It is more expensive and more difficult to obtain a mechanical patent. 2) Is there already an existing patent, perhaps made by the original designer or someone else? Patent searchs are not fool proof. I have a design patent on my Wenger Sundial, issued after a patent search. Fred Sawyer was able to point to earlier patents that were not found in my patent search and they should have been. I think that they do not invalidate my patent but the fact that they were missed is important. 3) Is it worth the cost of obtaining a patent? True, one wants to protect ones efforts but is the market for sundials that hot? A patent is only usefull if you are willing to defend it. That can be a very costly process. If my Wenger Sundial were copied I have the feeling that the broadened awareness of the design would probably make my dials only more interesting to the public. 4) Assuming that you want to proceed with a patent and that one seems reasonable then the only action that would make me confortable, if I were in your shoes, would be to approach the original designer with an offer of joint ownership of the patent. This would avoid possible conflicts in the future and definitely avoid conflicts of the soul. Regards, Dan Wenger Hello all: Hope all you Americans had a wonderful Thanksgiving! I have been having a discussion with a fellow dialist, who wishes to remain anonymous at this point, about copyrights and patents. Maybe some of you have also wondered about this before. Here is his dilemma : Let's say you read an article in The Compendium about someone's new idea for a sundial, and decide that you would like bring this design to life and enter into serious production of the sundial. Now the author of the published article only has drawings of his new sundial and presumeably no working model. You add several innovative features of your own to the original design and work out the manufacturing process. Now, after all this preliminary work, you are ready to begin production, and it occurs to you that maybe you should protect your project and efforts with a copyright or patent. But who has the legal rights to the finished sundial, the author of the original article or the manufacturer? Now I'm no lawyer, but I would assume that the original author wouldn't have published his new design if he didn't want the sundial to be built. Now I know that under copyright law that it's pretty much first come first served. In other words, the first person to apply for copyright or patent registration, regardless if he is the author or not, becomes the owner of the invention. I have heard horror stories of people who failed to obtain a copyright, and their ideas get stolen by someone else ( ie. the happy face logo, or the guy who invented in-line skates). But in this case, both parties have contributed their ideas to the final product. What should be done in this situation so that everybody wins and is happy with the outcome? Have any of you been faced with this situation, and what did you do to resolve it? Thanks, John Carmichael Tucson Arizona Daniel Lee Wenger Santa Cruz, CA [EMAIL PROTECTED] http://wengersundial.com http://wengersundial.com/wengerfamily Daniel Lee Wenger Santa Cruz, CA [EMAIL PROTECTED] http://wengersundial.com http://wengersundial.com/wengerfamily
Re: Darkness
Dear Dialists I can point out that my Wenger Sundial does show hours of sunlight. Once the position of the sun is found on the globe the declication of the sun has been found. Then by following the path of the sun during the day, keeping the declination constant, and going from the eastern horizon to the western horizon one may read off the hours that the sun is above the local horizon. As I recall, maritime twighlight is determined by the sun being less than 7 degrees below the horizion. This angle may be approximately read on my dial and thus the time of total darkness may be read. Dan Wenger At 07:14 AM 9/1/99 -0400, Mac Oglesby wrote: I wonder what it would take to make it a sundial showing hours until dark. That is, how would the time of dark (relative to sunset) be determined? Hi Mac, This is an excellent challenge. First, we have to define dark. Bowditch defines Civil Twilight as 0 to -6 degrees solar altitude, Nautical Twilight as 0 to -12 degrees and Astronomical Twilight as 0 to -18 degrees. This is why star gazing in the summer at my latitude (51) is so frustrating. We don't get the dark skies back until mid August. The limiting latitude for astronomical twilight on the solstice is 48.5 degrees. 90-23.5-18=48.5 I believe you could add horizontal lines to the virtual section of a sundial (when the sun is below the horizon) for -6, -12 and -18 degrees and see where the lines intersect the hour lines. Good programs like Zonwvlak trap these errors but my old spreadsheet programs were quite happy to calculate and plot these virtual lines. The brute force numerical solution would be to use the navigators' altitude equation and solve for the time angle t at altitudes of -6, -12 and -18 degrees. Sin Altitude = Sin Dec * Sin Lat - Cos Dec * Cos Lat * Cos t An approximation would be to estimate how long it takes for the sun to set to -6, -12 and -18 degrees based on psi,the angle of the setting sun with the horizon. When the altitude is zero, Cos psi = Sin Lat / Cos Dec. A useful approximation for the setting sun is psi is approximately equal to the co-latitude. The time for the sun to set is proportional to 1/Sin psi. This explains why tropical sunsets are so abrupt and northern sunsets are so mellow. It is not just the fact that time flies when you are having fun. I will be expanding on this theme at the NASS conference next month with a presentation on Sunset Phenomena. Or you could say it is dark when the street lights come on. When I was growing up in Norman Rockwell Land, when the street lights came on, it was dark and we all had to go home. Roger Bailey Walking Shadow Designs N 51 W 115 Daniel Lee Wenger Santa Cruz, CA [EMAIL PROTECTED] http://wengersundial.com http://wengersundial.com/wengerfamily
Re: sundial with a second hand
Discussions here and experiments of my own have established that shadow sharpener techniques allow a shadow position to be read with accuracy on the order of one second of time. This led me to look for a configuration that allows a continuous readout with this type of accuracy, not just the determination of one point in time (e.g., noon). Furthermore, in the hands-off spirit of sundials, I wanted to read the time by just looking, without having to fiddle with any instruments. Given a gnomon, ideally subtending an angle a bit less than that of the sun, a properly placed pinhole allows a very accurate determination of the time when the center of the shadow passes over the pinhole. Obviously, many such pinholes could be used, say one for each second of each minute. More elegant is to place this series of pinholes so close together that they overlap, resulting in a slit. The slit projects the sun onto a line of well-defined width. The shadow of the gnomon falls on a short section of this slit and blocks the sunlight. The result is a sharp-edged band of light intersected obliquely by a sharp-edged shadow. The position of the intersection moves along the band of light at a speed which allows, with proper set-up, resolution on the order of 1 second of time. With an appropriate scale, this can function as an indicator of seconds. To keep the dial compact, after a suitable period of time, e.g., 5 minutes, the shadow could pass onto a parallel slit that starts the process over again. This dial would be complex to build, and adjusting for the equation of time to 1 second accuracy would be an ordeal, but I think it must work and would be an intriguing project. I experimented a little with the principle using my clipboard on my window sill, but it is now too late in the afternoon for the sun to shine through my window. Looks like I'll have to go back to work. --Art Carlson Art I have been following the resent discussion with regard to the desire to make a sundial that can read in seconds. I would like to try to tie together the past three threads: Location of analemmas, precision and accuracy, and shadow sharpening techniques to read to within seconds. It may be that one can design a dial to be read to a precision of seconds, but the accuracy issue has still to be resolved. To recapitulate my earlier perspective. Analemic time lines for sundials may be thought of as projections of the analemmas that one may draw on the surface of the earth. The analemma may be thought of as a continuous curve through a set of points. Those points are determined by the geographical position of the sun at a given time of day for every day of the year. A curve through these 365 points is then projected onto a surface to get analemic time lines, a horizontal surface for a horizontal dial, a vertical surface for a vertical dial, etc. The point that I want to make is that the 365 geographical positions of the sun are not the same 365 points from year to year and they do not line on the same continuous curves from year to year. Thus the projected time line is not the same from year to year. What one does in practice is to take some sort of average to determine a useful time line for a usable sundial. If one is building a highly precise and accurate dial then the time line needs to be adjusted in some way to correct for the variation from year to year of the location of the set of 365 points that define the time line. Any goal of reading a sundial with accuracy of seconds has to allow for this adjustment. Without the adjustment one can perhaps achieve the desired precision but not the desired accuracy. Hope I have not cast a shadow upon desired projects. If I have addressed an issue that did not need addressing then I apologize. Dan Wenger Daniel Lee Wenger Santa Cruz, CA [EMAIL PROTECTED] http://wengersundial.com http://wengersundial.com/wengerfamily
Name of museum?
I have had an email that indicated that there is a director of a museum, who happens to be a member of NASS, who is putting together a sundial/clock exhibit for the millenium. Is there anyone on this list who might know who this person is? Many thanks. Dan Wenger Daniel Lee Wenger Santa Cruz, CA [EMAIL PROTECTED] http://wengersundial.com http://wengersundial.com/wengerfamily
Re: EOT=0
Hello John and everybody on this list, I don't want to extend this discussion endlessly , but I am surprised to read that the value of EOT depends on longitude. Perhaps I am totally wrong, but for me EOT is absolute. It is linked to the motion of Earth about the Sun and has nothing to do with longitude. Taking again Jim Cobb's formula, for any place on Earth : UT = Local Solar Time - EOT + 12 + Longitude(west is positive). The time when EOT = 0 is : UT = Solar Time + 12 + Longitude; or UT = Local Sidereal Time - AD + 12 + Longitude ;and : UT = Greenwich Sidereal Time - AD + 12 Longitude of the place has gone away. Am I wrong ? Best regards Jean-Paul Cornec . Jean-Paul I was involved some weeks ago (relative to the location of the analemma) with this issue and now view the issue as follows. When the EOT is zero the geographical position of the sun and the mean sun (longitude only) are the same. This happens at a particular moment, ie. a certain time. The time is the same for everyone, subject to time zone changes, and the event certainly occurs associated with a definite longitude. This longitude changes somewhat from year to year due to the fact that the earth's rotation is not coupled exactly to its location in its orbit about the sun. Hope I am clear and correct for everyone here. Dan Wenger Daniel Lee Wenger Santa Cruz, CA [EMAIL PROTECTED] http://wengersundial.com http://wengersundial.com/wengerfamily
New Pictures of Wenger Sundial
Dear Fellow Dialists I promised photos of my newest sundial and they are now on my web site. A set of pictures is at http://www.wengersundial.com/dialPicture.html The photo at http://www.wengersundial.com/dial1.html shows the detail of the analemma and the scribed features of the dial. This photo is relavent to the recent discussions of analemmas and their placement on sundials. On my globe the significance of the analemma is apparent. Each analemma represents the geographical position of the sun at mean time 6, 7, 8, 9, etc. for each day of the year. In fact the geographical postions of the sun at those mean time hours would be a collection of 365 dots but the analemma is interpolated to generate a semi continuous curve. Since the set of dots that would be generated during the following year would be slightly different the curve used represents some sort of average of the dots over a four year period. The generation of an analemma on another type of sundial involves a projection of these geographical positions through the origin of the globe onto some surface, usually a horizonal or vertical plane. The photos are detailed and my take some time to download. Hope you enjoy them. Dan Wenger
Re: Heliochronometers: Equation of Time
Thank you Chris for that nice amplification of my comments. My sundial has figure eight hour lines. The problem is where does one place the figure eight hour lines. My sundial is a globe of the earth with longitude lines indicated every 15 degrees. The figure eight hour lines are placed on the globe at a slight displacement from the 15 degree lines. The issue is that the placement varies from year to year. I believe that the periodicity of this placement is a similar one to that in the EoT error, if not one and the same. Am I missing something here? Dan Wenger 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]) === Daniel Lee Wenger Santa Cruz, CA [EMAIL PROTECTED] http://wengersundial.com http://wengersundial.com/wengerfamily
Re: Polaris time
Hello Dialists : I've got a question that's always bugged me. As I'm more of an artist than mathematician, I doubt that my answer is the correct one and I'm sure many of you geniuses out there know the answer. I'm sure many of you have seen time lapse photography of the little circle that Polaris circumscribes around the North Celestial Pole in the northern night sky. This is because it is about 1/2 a degree away from the N.C.P. If you orient your sundial north by Polaris when it is on the meridian, then there will be no time error, because the dial will be pointed due north. Right? But if you orient it when it is due east or west of the meridian, the sundial will be turned the maximum distance from true north (1/2 degree) and the maximum time error will result. How large is this error in seconds of time? Here's how I tried to solve it: If the sun moves 15 deg./hr. then it moves 15 deg./ 60 min.= 1 deg./.25min.=1 deg/15 sec.=.5 deg./7.5 sec. Is this the answer: 7.5 seconds? I've got a feeling that I've oversimplified the problem. I bet the answer turns out to be some bellcurve with an error which changes throughout the day. It's probably something only T.J.Lauroesch and J.R.Edinger,Jr. can solve! John Carmichael John You have over simplied. The error in time read with such an error in placement depends upon the location that the dial was made for and the time of year and day. I suspect, without further detailed analysis that the error that you give is close to the upper limit. For a sundial made for a location in the tropics the sun passes directly overhead a some times during the year. On those occasions the dial will read correctly no matter what the orientation of the dial. So the error due to error in placement is somewhere between 0 and some upper limit. Dan Wenger Daniel Lee Wenger Santa Cruz, CA [EMAIL PROTECTED] http://wengersundial.com http://wengersundial.com/wengerfamily
Re: Wood for dials
I have used teak for the base of my sundial. Pictures are on my web site. It is nice to work with but does need care. Wood, if available to the public will end up with John loves Mary engraved in it. If I were to want a durable exterior wood I would choose Koa. Hard to work with but very durable. It is used on the bed of trucks and is the prefered wood for that purpose. It is really quite a beautiful wood as well. Not sure if Koa is available in Europe or elsewhere. I believe that its native habitat is Hawaii. Dan Wenger Daniel Lee Wenger Santa Cruz, CA [EMAIL PROTECTED] http://wengersundial.com http://wengersundial.com/wengerfamily
Wenger Sundial
Hello dialists, May I bring your attention to my new web pages showing pictures of my Wenger Sundial. The models shown were made in the 70s. I will have photos of my new glass version in January. I have wanted to make this sundial in glass since the 70s but did not have the resources until now. Have been working on the laser programming and jig design for a year and have now my first glass version. Hope that you will be excited by the design. Dan Wenger Daniel Lee Wenger Santa Cruz, CA [EMAIL PROTECTED] http://wengersundial.com http://wengersundial.com/wengerfamily
