Re: Question about analemmic sundials
Hi, Troy! > I'm curious about analemmic sundials. Is it possible to move the gnomon of > the dial (along an analemma course marked with the proper days) to achieve > the same effect? I wonder since the analemma would likely be confusing to > laymen viewing the dial. Well, if we're talking about the same type of dial, that's the exact point... The hour points are leyed out on an ellipse whose shape depends on the latitude. The date line is just that, a line, on the North-South (minor) axis. The spacing of the dates is, I believe, the same as the projection of the dates on an analemma, onto the axis. The gnomon, which is commonly the observer, stands vertically on the date point, and the shadow extends towards the hour points at all seasons. Dave
RE: Question about analemmic sundials
Troy [EMAIL PROTECTED] asked < I'm curious about analemmic sundials. Is it possible to move the gnomon of the dial (along an analemma course marked with the proper days) to achieve the same effect? > If I understand Troy correctly, to be asking about simple dials with "figure eight" analemmas on the hour lines, I think the answer is "no" as what is wanted must affect all the hour lines equally, which could be achieved by a rotation of the dial about the gnomon axis, and I believe no displacement of the gnomon will achieve this. I'm open to correction, though! Andrew James N 51 04 W 01 18
Re: Question about analemmic sundials
Hello Troy: Are you talking about an "analemmic" dial or an "analemmatic" dial? John Carmichael >I'm curious about analemmic sundials. Is it possible to move the gnomon of >the dial (along an analemma course marked with the proper days) to achieve >the same effect? I wonder since the analemma would likely be confusing to >laymen viewing the dial. > >Thanks, >Troy > >
Re: Question about analemmic sundials
Thanks, that answers my question. In a message dated 12/12/00 10:40:34 AM Eastern Standard Time, [EMAIL PROTECTED] writes: << Troy, In issue 5-1 of the NASS Compendium there is an article by Yvone Masse about such a dial. The dial face is a straight line with hour marks. The gnomon is a string (or movable rod) that is attached to a pole at one end, The other end is set to a point on a figure 8 according to the date thus giving the correction for the EOT. ++ron >>
RE: Question about analemmic sundials
Ron Anthony has kindly given me a brief explanation (see below) of the movable style mean time dial to which he referred and pointed me to Yvon Masse's web site where there is a full description of this interesting and ingenious dial. The English version of a relevant page is at http://www.apro.fr/usr/ymasse/anmn2.htm Andrew James Ron Anthony [EMAIL PROTECTED] wrote: Here is my explanation of what he was saying. 1. Set up an armillary dial with a horizontal surface under it. 2. Pick a point (O) on the equatorial ring, say OPPOSITE from the 10 am hour mark. This point is the fixed point O in the diagram. 3. Project from that point through each of the hour lines onto the horizontal surface. This will result in a set of hour lines that are on a straight line. 4. By some math/graphical magic, he shrinks the size of the equatorial ring BUT keeps point O and one of the hour points. A projection of this new ring gives the same hour points on the horizontal surface. 5. By having the string always starting at point O and passing through the correct spot on the new pole style for each date he is able to shift the EoT. The other end of the string is determined by point O and the correct spot on the style. In practice the dial could be a post where the top is O, and the hour lines and analemma are painted on the ground. Simple dial, No? Compendium 5-1 contained a BASIC program to draw it. ++ron
