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26 lines
920 B
26 lines
920 B
<sect1 id="ai-horizon">
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<sect1info>
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<author>
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<firstname>Jason</firstname>
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<surname>Harris</surname>
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</author>
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</sect1info>
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<title>The Horizon</title>
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<indexterm><primary>Horizon</primary>
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<seealso>Horizontal Coordinates</seealso>
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</indexterm>
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<para>
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The <firstterm>Horizon</firstterm> is the line that separates Earth from Sky.
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More precisely, it is the line that divides all of the directions you can
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possibly look into two categories: those which intersect the Earth,
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and those which do not. At many locations, the Horizon is
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obscured by trees, buildings, mountains, &etc;. However, if you are on
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a ship at sea, the Horizon is strikingly apparent.
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</para><para>
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The horizon is the <firstterm>Fundamental Plane</firstterm> of the <link
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linkend="horizontal">Horizontal Coordinate System</link>. In other
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words, it is the locus of points which have an <firstterm>Altitude</firstterm>
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of zero degrees.
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</para>
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</sect1>
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