Later, as the months wear on, a series of additional messages arrive from Gerry -- always delivered in the most remarkable and surprising of ways. With each new message comes a new adventure, and each letter signs off in the same familiar way: P.S. I love you..
For a person standing at sea level, however, the horizon is only about 3 miles away. Lets do the calculations. The figure below shows an observer whose eyes are a distance E above sea level. A straight line drawn from the observers eyes tangent to the seas surface touches it at the distance d1, which is the distance to the horizon. If R is the radius of the earth, then, to first order in E/R, it is easy to show that.
But. h / 5280 is much smaller then 2r, hence 2r + h / 5280 is approximately 2r and thus. Substituting r = 3963 miles give the neat result that if your eyes are h feet above the earth, then the distance to the horizon IN MILES is about. Thus a person 6 feet tall standing on level ground can see for about 3 miles. So, theoretically, a person 6' tall (with binoculars) should be able to see the top of the head of a six-footer who is 6 miles away. He would see the whole person at a distance of 3 miles. Chris.