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as defined in astronomy, which takes account of the terrain and depth to the centre of Earth at a ground observer's location. The hour circles, specifically, are perfect circles
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An astronomical meridian follows the same concept and, almost precisely, the orientation of a meridian (also known as
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at any time. The hour circle is a subtype whereby it is expressed in hours as opposed to degrees,
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Diagram illustrating the definition of the hour circle of a star
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159:Declination
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