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.
The square root of 9 = 3. So, the horizon is about 3 miles away. Note: This simplified formula is quite accurate, but only works if the height is in feet and the distance in miles. If you want to use height in meters and distance in kilometers, you need to change the multiplier from 1.5 to 12.74.