Hi Fred You wrote: > John, > > Your proposed experiment suffers from the problem that the error is not > constant throughout any given day. Indeed, if it were, then the analemma > could in fact be used to correct for EOT. The problem is that when one > stands on the analemma, the error that gets introduced varies significantly > not only from day to day but also from hour to hour within a given day. So > there doesn't seem to be a lot of point in doing the experiment. At best, > it would only tell you the error in reading at that time on that particular > day. Wait a few hours and the error will be very different. > Yes of course you are right about the error being different at different times and dates.
What if I modify the experiment to show what you said is true? Instead, we could take simultaneous time readings from two plumbob/string gnomons, one placed over the meridian and the other placed over the analemma. The time readings could be done every hour on the date we are interested in testing. Is my thinking correct that Nov. 1st would produce the greatest error? If so, I wonder what time on Nov. 1 would the error be the greatest? 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> ----- Original Message ----- From: "fwsawyer" <[EMAIL PROTECTED]> To: "John Carmichael" <[EMAIL PROTECTED]> Sent: Wednesday, March 20, 2002 9:19 AM Subject: Re: Analemmatic Design Error > John, > > Your proposed experiment suffers from the problem that the error is not > constant throughout any given day. Indeed, if it were, then the analemma > could in fact be used to correct for EOT. The problem is that when one > stands on the analemma, the error that gets introduced varies significantly > not only from day to day but also from hour to hour within a given day. So > there doesn't seem to be a lot of point in doing the experiment. At best, > it would only tell you the error in reading at that time on that particular > day. Wait a few hours and the error will be very different. > > Actually, it is possible to include a pair of analemmas along the meridian > line to get a very close approximation to mean time. See the last figure in > my article: http://www.longwoodgardens.org/Sundial/Analemma.html > > Fred > > ----- Original Message ----- > From: "John Carmichael" <[EMAIL PROTECTED]> > To: "Sundial List" <[email protected]> > Sent: Wednesday, March 20, 2002 10:37 AM > Subject: Analemmatic Design Error > > > > 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> > > > > > > - > > > > -
