re: Arc de Triomphe

[Fabio Savian]

Hello, this is the first time I'm writing to this mail-list. Sorry for my english.   I think it is possible to built a sundial to know how long it will take to have the Sun in the middle of the Arc de Triomphe, or, in generic terms, to have the Sun at a given azimuth. It is a sundial with a conical gnomon like that for italic and babylonian hours but the cone is different and the hour lines too. Imagine the vertical plane which contains the Arc, this is an azimuthal plane, it contains the Sun when it has that azimuth. Now revolve this plane around the polar axis, this operation is the same to get the conical gnomon revolving the horizontal plane around the polar axis. Also in this case you will generate a cone, its vertix angle is the double of the elevation of a polar style placed on a wall which lies in the azimuthal plane. Now I can design a sundial with this "azimuthal hours", the dial may have any orientation and I have calculated the direction of the "azimuthal hour lines" with spherical trigonometry. This sundial is suited to wait for the Sun in a given azimuth, for example, on a street among skyscrapers, but if I want to watch the Sun in the middle of the Arc de Triomphe it must be the sunset too, so I have also to know the days it happens. I designed a sundial with two cones, one for the 'azimuthal hours' and another for the italic one. When the two sundials indicate the same time, the time to reach the azimuth and the time to the sunset, that is a right day.   Really the Sun in the Arc is not at the sunset, it has an altitude (about 2° 30') and I would have to calculate the rifraction adjustment, however I think this may be a new way to expect a Sun appointment.   I have done two pictures to explain this idea, you can find them at www.nonvedolora.it/experiments.htm   ciao Fabio Savian, Italy, [EMAIL PROTECTED]   PS while I'm writing this message I'm listening the TV about Columbia Shuttle,    I'm very sad...