



 
Hi Rita, If you draw a diagram you realize that the line of sight from the camera to the horizon is tangent to the surface of the earth and hence in the diagram below the angle CAB is a right angle.
What trig function relates r, r + h and the angle BCA? This gives you an equation that relates h and theta. The observable distance d is the length of the arc from E to A. What is the equation that relates the arc length, the radius r and the angle theta? Penny  


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