Dear John,
The logic of math will get you the right answer. The classic equation for
the altitude of the sun, well known by navigators and dialists is the
cosine rule of spherical trigonometry. sin (altitude)=
sin(latitude)*sin(declination)+cos(latitude)*cos(declination)*cos (time
angle).
For sunrise or sunset, the altitude is zero (ignoring refraction,
semi-diameter etc.) Recognizing that tan=sin/cos, this zero altitude case
reduces to;
cos(time angle)= -tan(latitude)*tan(declination).
This relatively simple equation will let you solve for rise and set times,
length of day etc. for any latitude or solar declination.
Enjoy,
Roger Bailey
Walking Shadow Designs
Canmore, Alberta, Canada
At 08:23 PM 3/2/98 GMT, you 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 -"-"-
>
