Correct. From the same formula, one can calculate that an observer at 200 ft above the surface would see the "base" of the turbine at a distance of 30.2 miles, therefore all of it. The tip would disappear at a additional distance of 42.6 miles, or 72.8 miles in total. Roger On 21 Mar 2010, at 2:35 PM, Rich Mason wrote: > 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 > Roger Eichhorn Professor Emeritus University of Houston eichhorn@xxxxxx
