Re: equation of time sundial
Ken, Your original mail has the sentence: * It seems to me (Ken) that it should be possible to build such a dial, since the EOT is a function of date, and date lines can be read from many sundials. In principle, I can just re-label the date lines with corresponding EOT values and interpolate. * I agree with this and a sample of a dial that's suitable is in Copenhagen, Denmark. See the website of De Zonnewijzerkring. Address below. Follow: Archives 2003 - 2013 Sundial of the month 2006 06-09 Copenhagen. Lable te datelines for a half year left and the other half year right with the appropriate equation of time rounded to e.g. one minute. The dial in Copenhagen has three scales so it can be used for many hours of the day. Best wishes, Fer. Fer J. de Vries De Zonnewijzerkring http://www.de-zonnewijzerkring.nl Molens http://www.collsemolen.dse.nl Eindhoven, Netherlands lat. 51:30 N long. 5:30 E - Original Message - From: jmikes...@ntlworld.com To: Ken Baldwin ; sundial@uni-koeln.de Sent: Monday, February 04, 2013 9:59 AM Subject: Re: equation of time sundial Ken, I’ve found a couple of small photos of my rather crude device. I’ve posted then in Dropbox at : https://www.dropbox.com/sh/tkxqw7x5mbr1axd/tYOlNAwT60 By coincidence, the 2nd photo shows the EoT is –7.5 minutes and sun’s declination is –7.5 degrees. I hope that makes things clearer. Of course, it’s just really a reverse engineered heliochronometer where you drive the alidade round using a 24 hour clock mechanism (widely available), to keep the spot of light on the analemma. However, I’ve used a graph of EoT and declination instead so that you can read off the two figures directly. Over the course of a year, the spot of light will trace out the analemma. Mike Shaw 53º 22' North 03º 02' West www.wiz.to/sundials No virus found in this message. Checked by AVG - www.avg.com Version: 2013.0.2897 / Virus Database: 2639/6078 - Release Date: 02/03/13 -- --- https://lists.uni-koeln.de/mailman/listinfo/sundial --- https://lists.uni-koeln.de/mailman/listinfo/sundial
Re: equation of time sundial
Ken, I’ve found a couple of small photos of my rather crude device. I’ve posted then in Dropbox at : https://www.dropbox.com/sh/tkxqw7x5mbr1axd/tYOlNAwT60 By coincidence, the 2nd photo shows the EoT is –7.5 minutes and sun’s declination is –7.5 degrees. I hope that makes things clearer. Of course, it’s just really a reverse engineered heliochronometer where you drive the alidade round using a 24 hour clock mechanism (widely available), to keep the spot of light on the analemma. However, I’ve used a graph of EoT and declination instead so that you can read off the two figures directly. Over the course of a year, the spot of light will trace out the analemma. Mike Shaw 53º 22' North 03º 02' West www.wiz.to/sundials - No virus found in this message. Checked by AVG - www.avg.com Version: 2013.0.2897 / Virus Database: 2639/6078 - Release Date: 02/03/13 --- https://lists.uni-koeln.de/mailman/listinfo/sundial
Re: equation of time sundial-heliochronometre 2
Hi, You can also see a magnificent heliochronometre made by John Carmichael at: http://www.flickr.com/photos/jlcarmichael/3576166915/in/set-72157618973847752/ best wishes, Peter On 4/02/2013 3:13 PM, Ken Baldwin wrote: Thanks, everyone. I see now how an analemmic gnomon can be used to read the EOT, if the equatorial band shows both mean and apparent time and you do the subtraction in your head. I'm most interested, though, in something which allows a direct reading of EOT... Mike, your solution sounds very interesting, but I confess I don't really understand it :-) I take it the motor is to keep the hole pointed toward the sun. Presumably this could be done manually, as on a shepard's dial? I'm unclear though on what's drawn inside. Is it a single curve of EOT as a function of declination, or a family of curves? Ken On Sun, Feb 3, 2013 at 12:02 PM, Ken Baldwin mailto:kenneth.bald...@gmail.com>> wrote: Hello, I'm a new list member, and have a beginner question: Are there examples of sundials whose sole (or primary) purpose is to compute the Equation of Time for the current date? - I know that this information is often provided as a graph in the furniture, but why should I have to know the date and perform the look-up manually? Can't I use the position of the sun to do the computation for me? - I know that the EOT correction can be incorporated into the layout of (some) hour lines, but I'm more interested in having dials which show true solar time. I'd like a separate device dedicated to computing the EOT. - I know that I can construct an analemmic noon mark to show the EOT for that day, since it's simply the east-west component of the analemma, but I'd like a design that can be read at any daylight hour. It seems to me that it should be possible to build such a dial, since the EOT is a function of date, and date lines can be read from many sundials. In principle, I can just re-label the date lines with corresponding EOT values and interpolate. I hope that makes sense. But since I haven't seen anything like that in introductory sundial books, I must be missing something... Is it that the shadow length can't be read accurately enough to get a reasonably precise EOT estimate? Or is it just too hard to make a readable layout, given that solar altitude is ambiguous between two dates, and that the component of the EOT due to the eccentricity of the earth's orbit is out of phase with the equinoxes and solstices? Thanks in advance, Ken Baldwin Corvallis, OR USA --- https://lists.uni-koeln.de/mailman/listinfo/sundial -- -- Peter Mayer Politics Department The University of Adelaide, AUSTRALIA 5005 Ph : +61 8 8313 5609 Fax : +61 8 8313 3443 e-mail: peter.ma...@adelaide.edu.au CRICOS Provider Number 00123M --- This email message is intended only for the addressee(s) and contains information that may be confidential and/or copyright. If you are not the intended recipient please notify the sender by reply email and immediately delete this email. Use, disclosure or reproduction of this email by anyone other than the intended recipient(s) is strictly prohibited. No representation is made that this email or any attachments are free of viruses. Virus scanning is recommended and is the responsibility of the recipient. <>--- https://lists.uni-koeln.de/mailman/listinfo/sundial
Re: equation of time sundial
Ken, You wrote: <> It’s to keep the cylinder pointed in the direction that the sun would be if it kept standard time. I should have added that this device includes the longitude correction as well. <> It’s a very simple straight line grid with the vertical lines showing minutes from standard time and the horizontal lines showing the sun’s declination from the equinox position. I hope that’s clearer. I’ll see if I can find any photos and contact you off list. Mike Shaw 53º 22' North 03º 02' West www.wiz.to/sundials - No virus found in this message. Checked by AVG - www.avg.com Version: 2013.0.2897 / Virus Database: 2639/6078 - Release Date: 02/03/13 --- https://lists.uni-koeln.de/mailman/listinfo/sundial
