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33 lines
1009 B
33 lines
1009 B
13 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
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>Jason</firstname
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> <surname
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>Harris</surname
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> </author>
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</sect1info>
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<title
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>Great Circles</title>
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<indexterm
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><primary
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>Great Circles</primary>
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<seealso
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>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 <link linkend="ai-csphere"
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>Celestial Sphere</link
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>. The intersection of any plane with the sphere will result in a circle on the surface of the sphere. If the plane happens to contain the centre of the sphere, the intersection circle is a <firstterm
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>Great Circle</firstterm
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>. Great circles are the largest circles that can be drawn on a sphere. Also, the shortest path between any two points on a sphere is always along a great circle. </para
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><para
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>Some examples of great circles on the celestial sphere include: the <link linkend="ai-horizon"
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>Horizon</link
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>, the <link linkend="ai-cequator"
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>Celestial Equator</link
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>, and the <link linkend="ai-ecliptic"
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>Ecliptic</link
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>. </para>
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</sect1>
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