Frank describes what can be seen on my website on page http://www.wijzerweb.be/maaseik002A.html The text is in Dutch but the images speak for themselves.
Willy Leenders Hasselt in Flanders (Belgium) Visit my website about the sundials in the province of Limburg (Flanders) with a section 'worth knowing about sundials' (mostly in Dutch): http://www.wijzerweb.be Op 3-dec-2010, om 11:25 heeft Frank King het volgende geschreven: > Dear triplederby100 > > Some subscribers to this list have more > curious names than others :-) > >> I hope this is the right forum to post >> this question. > > Yes, we answer any questions to do with > beams of sunlight :-) > >> ...a friend of mine visited a European >> country where he visited a building... >> a beam of sunlight strikes a particular >> spot inside the building only once in a >> year, and only at a particular time of >> the day. > > You will hear many stories like this but > a little explanation is required before > you should believe what you hear... > >> I am hoping the experts here can explain >> how this is made possible - since I am >> not an expert at all in the sun related >> mathematics. > > You don't need to know any mathematics for > a simple explanation... > > Imagine staring at the sun (a bad idea) > all day from sunrise to sunset and doing > this every day for a year. > > You will see that it traces a path across > the sky and that this path is high in > summer and low in winter. > > Now imagine tracking the sun with a > telescope (an even worse idea unless > you have high-tech eye protection). > > You will see the same thing. You have > to swing the telescope round during the > course of the day to keep it tracking > the sun and you will have to point it > up and down too. > > Then, on some special date at some special > moment, you CLAMP the telescope so that > it permanently points at where the sun > was at that special moment. > > Given that the sun follows a different > path each day, you won't be able to see > the sun through the telescope again > until the sun is in the same position > as it was at that special moment. > > It would be nice to say that you would > have to wait a whole year, and then the > sun would be in the same position at > the same time of day and, for a fleeting > moment, you could see it again through > the telescope. > > This isn't quite the whole story because > if the telescope isn't too high-powered > you will probably see the sun for a short > period at (about) the same time for a few > days either side of the chosen date. > > Moreover, there will almost certainly be > a quite different date when the sun's > path is approximately the same as it is > on the magic date. > > Now, you don't need a telescope at all. > A fixed tube will do, or a collection of > bits of stonework and church furniture > and other things that happen to leave a > narrow gap that you could draw a straight > line through. > > These things are usually a disappointment. > Either, at the critical moment on the > critical day, the sun isn't shining or > on a quite different day the sun happens > to be in the correct direction and spoils > the story. > > Frank King > Cambridge, U.K. > > --------------------------------------------------- > https://lists.uni-koeln.de/mailman/listinfo/sundial > --------------------------------------------------- https://lists.uni-koeln.de/mailman/listinfo/sundial
