Hi Dave: Of course your comments about analemmatic dials are correct, but If you read the thread carefully you will see that when I wrote: >> Also, in order to be able to tell time with short shadows around noon in the >> summer and to accomodate short people, it will be very important to mark the >> hour lines as close as possible to the gnomon foot (where the people stand). >> Correct?
I am refering to the HORIZONTAL sundial proposed by Patrick and Henry and not an analemmatic! Sorry if this was confusing. John > >I may be wrong, and it would be wise to verify this with Fer or someone >else far more knowledgeable about analemmatic dials, but I see a problem >with your vision of the dial: > >Analemmatic dials, as we have been discussing them, do not have hour >*lines*. They have hour *points* only, on the periphery of the ellipse. It >is the "responsibility" of the human gnomon to be tall enough to cast a >shadow all the way to the points. This sets the scale of the dial >somewhat, as a truly monumental dial would require Paul Bunyon (or at >least Wilt Chamberlain) as a gnomon! You can't beat it by - > >* Drawing hour lines, from the hour points to the gnomon foot, because the >foot moves with the time of year. > >* Drawing several "nested" dials at different scales (major axis length), >because the entire dial, including the date line/scale, is proportional to >the major axis. While you could draw lines connecting the corresponding >hour points, the central date lines would be of different lengths, so the >"gnomon" wouldn't have a unique point on which to stand. > >This also messes up your thought of painting footprints for different >height users, because all users, regardless of height, stand on the same >(date) point. Some just have to extend their arms over their heads, to get >a long enough shadow. > >To some extent, the dial design corrects for the "shortcomings" of the >users. Note that the date points for Summer are much closer to the North >rim of the dial, and the hour points for Noon are much closer to the date >line than 0600 and 1800. These automatically correct for the varying >shadow lengths per time of day and time of year... > >Does this make sense? > >Dave Bell >N37.29W121.97 > > >
