Re: converting DeltaCad files
Hello all I use AutoCAD and if I'm not wrong it can output files in both of these formats. Will let you know when i'm home in some hours. Thanks alexei pace At 19:07 04/04/2000, Gordon Uber wrote: John, I would suggest saving the DeltaCad file in a standard CAD format (such as DXF or an AutoCAD format) and then running it through another CAD program which can output the HPGL2 or PLT file. HPGL (Hewlett Packard Graphics Language) is for HP printers/plotters; I do not know what PLT is: perhaps a Macintosh format? Conversion programs such as HiJaak can perhaps do the conversion also, but are a bit expensive. It would be appreciated if you let us know what solution you find. Best wishes, Gordon At 08:04 AM 4/3/00 -0700, John Carmichael wrote: Hi Ron (or anybody else who might know): I did some checking with a local print shop to see if they would be able to print large blueline copys of sundials drawn on DeltaCad. They can, I was told, if these files are in HPGL-2 or PLT form. I went to save as and these files are not listed as options. Do you know how to convert DeltaCad files into HPGH-2 or PLT files??? Thanks, John Carmichael Gordon Uber [EMAIL PROTECTED] San Diego, California USA Webmaster: Clocks and Time: http://www.ubr.com/clocks * The early bird gets the worm, but the second mouse gets the cheese!
RE: Analemma Stuff
Thibaud Taudin-Chabot wrote it is simple arithmetic: our watch shows mean time, so the mean of the correction should be 0, otherwise your watch is fast or slow after a year. I thought just the same when I first saw the question - but then I thought again. I believe that the above condition means that the average length of the day (or hour, minute, second ...) shown by solar time must be the same as by the mean sun or corresponding clock. But you could declare solar noon today - at the meridian or allowing for the difference in longitude - to be at 12:02 or 11:57 or at any other time without affecting the going either of the sun or the clock. Therefore one can offset the EoT curve by a fixed amount with impunity in this respect. In fact this is exactly what we do by adopting a time at a longitude different from our own - or still more drastically by introducing daylight saving. I believe that the EoT curve IS chosen so that the average IS zero, which is the same as saying that if both its two sinusoidal components were reduced in amplitude to zero, then it would lie along the straight line of zero correction. This is entirely logical as if the magnitude were zero then it would make no sense to have a non-zero EoT. Adding up the two sine waves, at frequencies of 1/year and 2/year with their different zero cross points and amplitudes, quite naturally results in the curve we know with its particular crossing points. These dates are therefore not arbitrary but derive from the relationships of the phases (as they relate to our calendar) and the amplitudes of the two contributing components of its cause, the orbital eccentricity and the inclination. Andrew James 01 18 W 51 04 N
Zero point on the Analemma Answer
I think Andrew James' explanation about the sum of two symmetrical curves (inclination and orbital eccentricity) may be exactly how the zero point for the equation of time was determined. There is a good article on this in Sky and Telescope, July 1972, pages 20-3 by Bernard Oliver. He breaks down the analemma into these two curves, each of which is appears to be symmetrically referenced around the zero point (EoT=0). He then demonstrates, as Luke Coletti points out, that these curves change over time, changing the overall shape of the analemma. He calculates that in 1246AD the analemma was a symmetric figure 8, with its intersecting point (where the 8 crosses itself) at EoT=0. Bill Gottesman Burlington, VT
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: Analemma Stuff
Luke, I really liked your clear explanation, but I think you meant to say the ANALEMMA has two components, the EOT and the declination. The EOT is not dependent upon the obliquity; we would still have it even if the axis were perpendicular to the ecliptic. Luckily, both independent components have a common, cyclical variable, the time of the year, and therefore have a single solution graph. Like you said, can you imagine the changing analemma if precession were only 100 years instead of 26,000 or so years!
Re: Analemma Stuff
I don't really know, but I would think that the zero level is chosen so that the total area of the EQT curve above the line matches that below the line. This would make the annual mean of the EQT would be zero minutes. At 23:02 3/04/2000 -0400, [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 Regards Hank de Wit Adelaide Australia 34.9231S 138.6206E B[EMAIL PROTECTED]/B
Re: Analemma Stuff
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
Re: Analemma Stuff
Hi Fritz, The analemma is in essence just a graph of the EoT vs Declination, in discussing the components of the EoT the analemma need not be mentioned, the analemma is just another way of expressing the EoT. The dynamics of the EoT define the shape of the analemma. As regards to the EoT not being dependent upon obliquity, I'm not sure what to say, other than it truly is. I can say that you are correct in saying that some value for the EoT would still exist if our axis of rotation was perpendicular to the plane of our orbit (zero obliquity), assuming that there is still eccentricity to the orbit. Also, the analemma fundamentally needs no correlation to date. The single solution you mention has to do with orbital position not the date. However, many (like me) include the date along the analemma and the short term variation of the leap year cycle will effect the placement of the date ticks. As regards to the variation of the EoT (changing shape of the analemma) requiring 26,000years, this too is incorrect. I've explained this in some length in earlier messages to the list. In short, the rate at which the Vernal Equinox approaches perihelion is approx. 50arc-secs/yr and the rate at which perihelion approaches the Vernal Equinox is close to 7 arc-secs/yr with a delta close to 1arc-min/yr! For example, the shape of the analemma was symmetrical in the 16th century, is it symmetrical now? Hmmm, what happened? Was the 16th century 26,000 year ago? Regards, Luke Coletti Fritz Stumpges wrote: Luke, I really liked your clear explanation, but I think you meant to say the ANALEMMA has two components, the EOT and the declination. The EOT is not dependent upon the obliquity; we would still have it even if the axis were perpendicular to the ecliptic. Luckily, both independent components have a common, cyclical variable, the time of the year, and therefore have a single solution graph. Like you said, can you imagine the changing analemma if precession were only 100 years instead of 26,000 or so years!
Creating .prn files for a plotter
Hi All, Here is a way to produce .prn plotter files directly from DeltaCad, or any CAD Program. These directions are for Windows98, but they should adapt to other Windows versions. Go to Control Panel | Printers. Select Add Printer, and follow the Wizard to install a Local Printer. From the list of Manufacturers: select HP (Hewlett Packard) From the list of Printers: select 7585A (It's a plotter). Click Next, and under Available Ports select File. Click Next - You may need your Win98 CDROM. If you opted to print a test page, type afilename.prn in the dialog. afilename.prn should appear in the folder you selected. There isn't much you can do with it unless you have a plotter. --- If all has gone well the 7585A plotter should appear in your pick list of installed printers, and any files sent to the 7585A plotter will actually be sent to disk as a .prn file. (You must include the extension.) The 7585A will accept paper sizes up to 34x44 inches. I would get together with whoever is going to plot your drawing to find out about scale etc. They may suggest you install a different plotter to correspond to whatever they use. I hope this helps, Bob
Re: Analemma Stuff
it is simple arithmetic: our watch shows mean time, so the mean of the correction should be 0, otherwise your watch is fast or slow after a year. At 23:02 3-4-00 EDT, you wrote: -Original Message/Oorspronkelijk bericht-- 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 - 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)
