François BLATEYRON wrote: > > Dear all > > I am rechecking all the equations used in my program Shadows, just to be > sure it works in any case for both north and south hemispheres. > > I am wondering if the horizontal co-ordinates are set the same way for both > hemispheres : > > in the north, the Azimut co_ordinate is the horizontal angle taken from the > local meridian, in the retrograde way. So it is positive toward the West. > The Height co-ordinate is positive above the horizon. > > For the south, does the definition of azimut say it is also retrograde (so > positive towards the East), or is it the same direction as in the north. In > this case, the trigonometric equations to convert from equatorial > co-ordinates to horizontal co-ordinates need to be modified. > > Is there a book that explains astronomical calculations for the south > hemisphere? > > Thanks a lot for your help. I hope my bad english is understandable > enough... > > François Blateyron > [EMAIL PROTECTED] (home) / [EMAIL PROTECTED] (pro) > Home page: http://web.fc-net.fr/frb/ > Cadrans solaires / Sundials: http://web.fc-net.fr/frb/sundials/vvisit.html
Hello François, To my opinion it isn't important what system for azimut you choose in your computerprogram, but it is more important to use the same system in the northern and southern hemisphere as well. In navigation the sytem with azimut = 0 at north is used and azimut is counted positive to the east. And this system is used all over the world. In my computerprograms I use azimut = 0 at south because in gnomonics it was usable to do so. To the west than is positive. To be universal all over the world I use this system also on the southern hemisphere. If the once chosen definition is mentioned in the program anybody easily can convert "his" system into the system of the program. If you choose to make different definitions for the northern and southern hemispheres you have a problem at latitude 0 degrees. Is that northern or southern hemisphere? Also at that latitude I do hope people like to build sundials....... My advice is just to choose a system convenient to you but use it all over the world. Fer.
