John Butler wrote: > > This may seem a very silly question but here goes.. > > What is the behaviour of the sun path through the year in the tropics? > > The following description of the problem may be so shot with misconceptions > that the question itself may be the problem, but.... > > As I understand it, taking an Earth-centred view from northern latitudes, the > Sun's path steadily rises in the sky till the summer solstice at which point > the sun is straight overhead at the tropic of Cancer. It then sinks in the > sky until the winter solstice at which point it is directly overhead on the > tropic of Capricorn. > > If that is true, then between say the equator and the tropic of Cancer the > sun is directly overhead twice in the year, once as it 'heads north' to the > tropic of Cancer and again as it 'heads south' past the equator. On this > basis, > any point between the tropics has two longest days in the year and at a point > infinitessimally close to the equator the (marginally) longest days are at the > equinoxes. > > Is this true or am I tangled in my own logic?... > > .. and thanks to "Sundials on the Internet" for pointing me at this list .. > > John Butler email: [EMAIL PROTECTED] ___ > Department of Computer Science WWW: http://www.dcs.ed.ac.uk/home/jhb (ovo) > University of Edinburgh phone: (+44) (0)131-650-5181 > ((`-')) > Edinburgh EH9 3JZ, UK. fax: (+44) (0)131-667-7209 -"-"-
Dear John Butler, Between the tropics the sun reaches its highest point of 90 degrees if the sun's declination is the same as the latitude, but this isn't the longest day. The longest day is at the solstices, with declination 23.5 (north lat.) or - 23.5 (south lat.) degrees. Except for latitude 0 degrees: all days are 12 hours long. Use the formula cos T = - tan lat * tan decl T is half the length of the day in degrees lat is latitude decl is the sun's declination. Another aspect of the sun's path between the tropics is the retrogradation of the shadow. If the sun can reach north ( for north lat.) then the shadow on an horizontal plane reaches twice the same azimuth. First the shadow moves in one direction and than the shadows moves in the opposite direction. This happens in the morning as well in the afternoon. To read an analemmatic sundial than gives problems...... This is a nice aspect to experiment with. Make such an analemmatic sundial and place it at your latitude, but tilted of course. Then you may see the retrogration of the shadow. Fer de Vries Netherlands.
