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.
Mountains, trees, and other elevated features are not considered part of the geographic horizon. The sea-level horizon is the geographic horizon at sea level. One of the best places to see the sea-level horizon is a beach. The ocean and the sky provide a clean, flat line where the Earth seems to meet the sky.