TITLE: How far can one see over the ocean?
QUESTION [53 upvotes]: Since Earth is a sphere, one has only a limited visibility radius. How far is that, actually?
This Q&A was inspired by this question, about whether or not Legolas can see the 24km distant Riders of Rohan.

REPLY [8 votes]: If you go sailing, you'll have about 5 nautical miles of visibility (1nm = 1852m). I personally find the nomogram a delightful invention:

Simply draw a straight line between the height of the observer and the height of the object on the horizon (in this case = 0), then read off the geographical range.