Thibaud Chabot
At 08:37 20-03-2002 -0700, you wrote:
Hello All After much discussion I was finally able to convince the directors of Flandrau Planetarium that their sidewalk analemmatic sundial is incorrectly painted because it lacks a meridian line. Instead, It has an analemma on the meridian and people are instructed to stand on the analemma. Thank you Frans Maes, because the information in your website was very helpful in explaining this common design error.(Frans W. MAES <[EMAIL PROTECTED]>). You can view a foto of this dial at www.sundials.org/registry, dial #13, Tucson Arizona). I had an idea for an experiment that will determine the amount of time reading error caused by this design flaw. Here is a copy of an email I sent Flandrau. Would any of you analemmatic experts look at this and let me know if my thinking is correct on this: Here's my letter to Flandrau: <I'm glad that you were able to digest all that information on Analemmatic sundials and that you are convinced of the Flandrau analemmatic design error. It's a complicated subject and difficult to grasp for most people. By the way, if you look closely at the photo of the Flandrau Analemmatic on the NASS Registry, you can see the meridian line, and a little girl is standing on it. The colors of the paint look bright and new. This is an old picture that Chad found. This makes me think that the original design had the meridian line and that it was probably not painted in a subsequent renovation. I have an interesting idea for an experiment that will tell you the amount of error in minutes of time caused by standing on the analemma instead of the meridian. (It would be a great project for some school kid). The amount of error observed is date dependent. On those dates when the Equation of Time is zero, there is no error. Procedure for the Experiment: 1. Pick a date for the experiment when the analemma DOES NOT cross the meridian.(i.e.. Do not do the experiment when the Equation of Time is zero). The best day of the year to do the experiment is November 1st because The Equation of Time is at its maximum, -16 minutes. If you look at the analemma, you will see this date on the right-hand (east) side of the upper (northern) lobe where the distance to the meridian is maximum. 2. Instead of using a person's shadow, for greater precision, use a plumbob on a six foot string. 3. At any time during the day of the experiment, compare the time readings of the string's shadow when the plumbob is over the analemma and when it is over the meridian. Subtracting the time readings gives the amount of error in minutes. To fix your dial, you need to paint the meridian line! You can leave the present analemma as is, but to avoid confusion, the users need to know where to stand. They should be instructed to locate the current date on the analemma, then stand on the closest point on the meridian to the left or right of the date on the analemma. Or, you can completely get rid of the analemma, paint in a meridian line with dates, and give people the simpler instructions of standing on the date.> Thanks for your thoughts on this. John John L. Carmichael Jr. Sundial Sculptures 925 E. Foothills Dr. Tucson Arizona 85718 USA Tel: 520-696-1709 Email: [EMAIL PROTECTED] Website: <http://www.sundialsculptures.com> -
--------------------------------------------------------------------- Thibaud Taudin-Chabot 52° 18' 19.85" North, 04° 51' 09.45" East, alt. -3.45 m home email: [EMAIL PROTECTED] -
