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 Good luck with your dial project, Bill
