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.
When in a tall building, the horizon can be as far as about 40 miles. From the ISS, the distance to the horizon is over 1000 miles. So from horizon to horizon, the section of the Earth you can see at any one time is a patch about 2000 miles across, almost enough to see the entire United States at once.