NavList:

Bob, I'll write a more detailed reply later, but while I'm thinking about it, one of the things I haven't seen discussed in standard resources is the "depth" of the horizon. When we look out at "the" horizon, of course we're seeing some range of overlapping wavetops. But just how large is the region that overlaps to create the visible horizon. Imagine my height of eye is 25 feet. The standard quoted distance to the horizon 1.16 · sqrt(25) or 5.8 nautical miles. Now suppose I place three buoys in a row aligned one more or less in front of the other as seen from my shore location at distances of 5.3, 5.8, and 6.3 nautical miles. Also, let's suppose the buoys are different colors and shapes but they each show about one foot of height above the water. Looking through binoculars, they would all three appear to be "on" the horizon, bobbing up and down and occasionally disappearing behind waves. It would be difficult to say which one of them is "really" at the horizon distance by observation. The horizon has depth.

Frank Reed