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28 lines
966 B
28 lines
966 B
15 years ago
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<sect1 id="ai-cequator">
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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 Celestial Equator</title>
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<indexterm><primary>Celestial Equator</primary>
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<seealso>Equatorial Coordinates</seealso>
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</indexterm>
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<para>
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The <firstterm>Celestial Equator</firstterm> is an imaginary <link
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linkend="ai-greatcircle">great circle</link> on the <link
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linkend="ai-csphere">celestial sphere</link>. The celestial equator
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is the fundamental plane of the <link linkend="equatorial">Equatorial
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Coordinate System</link>, so it is defined as the locus of points
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with Declination of zero degrees. It is also the projection of the
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Earth's equator onto the sky.
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</para>
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<para>
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The Celestial Equator and the <link linkend="ai-ecliptic">Ecliptic</link>
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are set at an angle of 23.5 degrees in the sky. The points where they
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intersect are the Vernal and Autumnal <link
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linkend="ai-equinox">Equinoxes</link>.
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</para>
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</sect1>
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