Defining the horizon is rather simple: walk out into the middle of a large, open field, or just imagine yourself standing there. Lift one arm until it is horizontal, or at 0° elevation, and point in any direction at the “line” where the sky meets the earth. This is a single point (see what I just did there?) on the horizon. Keeping your arm extended horizontally, turn about in a complete circle, or 360°, and the horizontal circle traced out by the extended finger has traced out all of the points that make up the horizon, which we will simply refer to as the horizon.


Image Credit:
Zenith. Addison Welsey. cse.ssl.berkeley.edu/ Accessed by Jim Johnson on January 19, 2015.

© James R. Johnson, 2015.

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