Don't forget to factor in the height of the observer's position. It's
one thing to be at lake level, another to be 200 feet up on a bluff.
Rich
On Mar 21, 2010, at 12:38 PM, Roger Eichhorn wrote:
Andy,
The tip of the turbine should disappear from view when it is located
a distance, along the circumference of the earth, c (away from the
observer), equal to the radius of the the earth, r, times the arcos
of the ratio of the radius of the earth divided by the radius plus
the height of the turbine, where the angle implied is measured in
radians. Taking r = 12,000 miles, this gives c = 42.6 miles for an
object 400 ft tall. The apparent height should be approximately
equal to the actual distance away divided by c times 400, in feet.
So, a turbine located 21.3 miles away should appear to be 200 ft
tall. I haven't worked out how this translates to image size, focal
length, etc.
Roger
