John, An azimuthal sundial with rings that are not in the sequence of the real dates will not have a closed curve.
In my program Spin you may choose between inner circle as january or as july. This overcomes a litlle the problem of the gnomon length. However, have in mind that any dial has its advantages and disadvantages. An azimuthal dial isn't very suitable at low latitudes and a dial based on measurement of the altitude of the sun isn't suitable at high latitudes. Best, Fer. Fer J. de Vries [EMAIL PROTECTED] http://www.iae.nl/users/ferdv/ Eindhoven, Netherlands lat. 51:30 N long. 5:30 E ----- Original Message ----- From: John Carmichael <[EMAIL PROTECTED]> To: <[email protected]> Cc: <[EMAIL PROTECTED]> Sent: Sunday, February 20, 2000 5:27 PM Subject: azimuthal gnomon length problem > Hello all: > > I've been having lengthy discussions with Fer, Sarah Edmonson and Steve > Lelievre about azimuthal (Dali) sundials. I have one more > observation/question that I'd like to make, but I thought I'd throw it out > to the List to get other people's input as well. > > We briefly mentioned that for the vertical gnomon's shadow to reach the > outer concentric date ring at mid-day, it would have to be extremely tall, > especially at lower latitudes. (Here in Tucson at 32.5 deg. N. , the sun is > only 9 degrees away from zenith on the summer solstice). Bill Gottesman > suggested using a string tied to the gnomon's foot to artificially extend > the shadow's length to to outer ring during the mid-day hours. > (A telescoping rod serving as the vertical gnomon, like a car antenna, might > work also). > > Here's another idea, but will it work? > > Another way to solve the gnomon height problem might be to make the inner > ring the June ring, when the sun is highest and the shadow the shortest. The > next ring would be July followed by May, August, April, Sept, March, Oct, > Feb, Nov, Jan, and December as the outer ring. This ring order would place > those summer short shadow months closest to the gnomon and the winter long > shadow months further out. This ring arrangement would increase the number > of hours where the shadow crosses the date lines and make the dial more > functional. > > However, arranging the date rings out of monthly sequence would make it > impossible to connect the hour lines in a nice curve. Instead, for each date > ring, wouldn't there just be a little time line segment, unconnected to to > hour line in the adjacent date ring? > > I'm wondering if my idea would work, and if so, if I can get Fer's spin > program to do it. > > any thoughts anyone? > > John Carmichael > Tucson Arizona > > p.s. for those of you still struggling to understand Dali and azimuthal > sundials, don't make the same mistake I did by confusing the terms "Azimuth > sundial" and "Azimuthal sundials". They aretwo completely different kinds of > sundials and are designed on Zonwvlak using two different programs!!! > >
