taken off the coast of Sicily, 2005
Nothing between you and the edge of the world
'Now there was no land to be seen, the horizon was a circle of water and the night sky was lit up by the moon.' J.W. Goethe 
'The discovery of the horizon reflects the historical experience that the known world is contained within it and an unknown world begins beyond it; both worlds should be explored.' Stephen Oettermann 
In the diary for his Italian Journey, Goethe recounts a sea voyage from Naples to Sicily undertaken at the end of March 1787, during which the vessel's progress was delayed as a result of adverse winds. An initial bout of seasickness confined the author to his cabin but the ensuing calm led him to describe the voyage as a 'decisive event'. Having arrived in Sicily after an extended trip, Goethe remembers the particular sensation of being surrounded entirely by water with no reference point other than the horizon. He describes this horizon (in W.H. Auden's translation), the singular perception of which profoundly affected him. 'No-one who has never seen himself surrounded on all sides by nothing but the sea can have a true perception of the world and his own relation to it. The simple, noble line of the marine horizon has given me, as a landscape painter, quite new ideas.'
One imagines the beleaguered vessel in the midst of the ocean as if seen from above with the observer occupying the centre of a vast circle indicating the limits of his vision. The simple, noble line of the horizon is straight and level when viewed from our usual vantage point five feet or so above ground - or sea - level but can be imagined, in the terms offered by Goethe's account, as a segment of the circumference of our visual field itself. On the circumference of this field, the horizon is merely the shortest distance between two points. Yet while its form in plan can be conceived of as an arc - a segment of the visual field - and in elevation as a straight line, any increase in the observer's altitude, a flight in an aeroplane for example, turns the line into an object. It begins to define the edge of the world.
The line of the horizon both indicates our relative proximity to the terrestrial surface of the globe and acts as the demarcation of the visible world. It is as much a function of vision itself as it is a property of the space external to us. In a sense, it will always maintain its distance and elude attempts to reach it: the horizon line represents absolute distance but this distance is as much an idea as a physical, visual experience. It hints at a realm existing beyond the limits of vision.
 J.W. Goethe, Die Italienische Reise, 30th March 1787; Italian Journey (trans. W.H. Auden & E. Mayer), London: Collins 1962, pp215-220.
 Stephen Oettermann, The Panorama: History of a Mass Medium, New York: Zone 1997, p13.
See also 'The Light Years' by Italo Calvino which comically explores the idea of an expanding cosmic horizon. Italo Calvino, Cosmicomics, (trans. William Weaver), San Diego & London: Harcourt Brace 1968.