Vanderlei and others, Please forgive my previous incomplete transmission on this topic:
>Vanderlei Borsari wrote: >>I have a doubt and I hope someone can help me: I would like to make a >>Shepherd´s (cilyndrical) dial, and I found the following equation to >>calculate the size of the gnomon: >>G = H cot(113,5º - lat) >>Where: G is the size of the gnomon >>H is the height of the dial scale >>lat is the local latitude >>The problem is that I live in a city over the capricorn tropic (23,5º), and >>it is not possible to calculate cot (113,5-23,5) = cot(90º). >Thank you >As you live on the Tropic of Capricorn, the noon sun will be vertical above >you at summer solstice. At winter solstice, noon sun will be directly above > the Tropic of Cancer, farthest away from your vertical by 2 x 23.5° = 47°. >So your gnomon's horizontal length G must be: > G = TAN (47°) x H = 1.0724 x H I should have gone on to point out that: "As you live on the Tropic of Capricorn, the noon sun will be vertical above you at summer solstice," implys that the gnomon tip's shadow is then parallel to the cylinder and scale, and so will never fall upon it. In short, a sheperds' (altitude) dial is not suitable for Mr. Borsari's location. Bill
