Hi guys, Thanks for your responses.
I'm not trying to read the EOT-adjusted time from the device, I want to read the actual EOT value itself for that date. For example, on Aug 9th, at any daylight hour, I'd like to be able to read, say, -5.5 min. Maybe I'm misunderstanding, but do I get that from these analemmic gnomons or hour lines? I'm suggesting something like Peter's design, but with the hour lines removed, and the date lines labelled with the EOT value (-15 min -> 15 min). I understand Simon's point that the altitude of the sun is ambiguous between two dates, so perhaps it would have to be split into two plates (like half-analemmas). Of course, this requires the user to know which 6 month period of the year they are in, which partially defeats the purpose of not needing to know the date :-) Ken On Sun, Feb 3, 2013 at 2:14 PM, Peter Mayer <peter.ma...@adelaide.edu.au>wrote: > Hi Ken, > > Here's another example of a dial which may interest you. This is > my adaptation of a brilliant dial coded by Steve Lelievre. To fit the size > limit on this list, I've had to squeeze the image greatly, but you should > be able to grasp the principle of the dial: each month is a separate > concentric circle. Between month lines one must interpolate the date to > read the civil time. > > > best wishes, > > Peter > > On 4/02/2013 6:32 AM, Ken Baldwin 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<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. >
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