How Far Away Is the Horizon?
The actual distance of the horizon away from us depends altogether upon the height above the sea level from which we are looking as far as we can. The horizon is always as far away as we can see. At the seashore, where we are practically on a level with the water, we cannot see so far as when we are up on a bluff or hill overlooking the sea. The higher we go up straight from a given point the greater the distance we can see up to a certain point and the farther away the horizon will appear. The height of the person looking, of course, figures in this, because when you are at sea level it is only your feet really that are at sea level (if you are standing up straight) and the distance of the horizon is measured from the eye of the person looking. A boy or girl of ten would be, say, a little over four feet high, and the eyes of such a person would be about four feet above the level of the sea. At that height the horizon would be about two and a half miles away. If the eyes are six feet above sea level the distance of the horizon will be about three miles, so that practically every one sees a different horizon, that is, one that appears at a different distance. A hundred feet above the level of the sea the horizon will be more than thirteen miles away, while at 1000 feet altitude it would be 42 miles away, and if you could go a mile into the air the horizon would appear 96 miles from where you are. The higher you go the farther away the circle which apparently marks the joining of the earth and sky appears.