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28 lines
992 B
28 lines
992 B
15 years ago
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<sect1 id="ai-greatcircle">
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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>Great Circles</title>
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<indexterm><primary>Great Circles</primary>
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<seealso>Celestial Sphere</seealso>
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</indexterm>
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<para>
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Consider a sphere, such as the Earth, or the
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<link linkend="ai-csphere">Celestial Sphere</link>. The intersection
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of any plane with the sphere will result in a circle on the surface of
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the sphere. If the plane happens to contain the center of the sphere,
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the intersection circle is a <firstterm>Great Circle</firstterm>.
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Great circles are the largest circles that can be drawn on a sphere.
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Also, the shortest path between any two points on a sphere is always
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along a great circle.
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</para><para>
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Some examples of great circles on the celestial sphere include: the
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<link linkend="ai-horizon">Horizon</link>, the
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<link linkend="ai-cequator">Celestial Equator</link>, and the
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<link linkend="ai-ecliptic">Ecliptic</link>.
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</para>
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</sect1>
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