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29 lines
1.1 KiB
29 lines
1.1 KiB
<sect1 id="ai-meridian">
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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 Local Meridian</title>
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<indexterm><primary>Local Meridian</primary>
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<seealso>Hour Angle</seealso>
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<seealso>Celestial Sphere</seealso>
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</indexterm>
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<para>
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The Local Meridian is an imaginary <link linkend="ai-greatcircle">Great Circle</link>
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on the <link linkend="ai-csphere">Celestial Sphere</link> that is perpendicular
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to the local <link linkend="ai-horizon">Horizon</link>. It passes through the
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North point on the Horizon, through the <link linkend="ai-cpoles">Celestial
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Pole</link>, up to the <link linkend="ai-zenith">Zenith</link>, and through the
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South point on the Horizon.
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</para><para>
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Because it is fixed to the local Horizon, stars will appear to drift past
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the Local Meridian as the Earth spins. You can use an object's <link
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linkend="equatorial">Right Ascension</link> and the <link
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linkend="ai-sidereal">Local Sidereal Time</link> to determine when it will
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cross your Local Meridian (see <link linkend="ai-hourangle">Hour Angle</link>).
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</para>
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</sect1>
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