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Sundial
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<p>A sundial is a <a href="/facts/Horology/u8CzMt1a">horological</a> device that tells the time of <a href="/facts/Day/MTAtWLDj">day</a> (referred to as <a href="/facts/Civil_time/DehyR1AL">civil time</a> in modern usage) when direct <a href="/facts/Sunlight/WPkJRC7s">sunlight</a> shines by the <a href="/facts/Position_of_the_Sun/rNhWtukM">apparent position</a> of the <a href="/facts/Sun/CadPCVHh">Sun</a> in the <a href="/facts/Sky/wwvQ84J1">sky</a>. In the narrowest sense of the word, it consists of a flat plate (the <i>dial</i>) and a <a href="/facts/Gnomon/J23dXDvD">gnomon</a>, which casts a <a href="/facts/Shadow/f9zpBgFQ">shadow</a> onto the dial. As the Sun <a href="/facts/Diurnal_motion/WXqqYtES">appears to move</a> through the sky, the shadow aligns with different hour-lines, which are marked on the dial to indicate the time of day. The <i>style</i> is the time-telling edge of the gnomon, though a single point or <i>nodus</i> may be used. The gnomon casts a broad shadow; the shadow of the style shows the time. The gnomon may be a rod, wire, or elaborately decorated metal casting. The style must be <a href="/facts/Polar_alignment/wq7mx4Uw">parallel to the axis</a> of the <a href="/facts/Earth%27s_rotation/mDbXcKUx">Earth's rotation</a> for the sundial to be accurate throughout the year. The style's angle from horizontal is equal to the sundial's geographical <a href="/facts/Latitude/IBYqkjhU">latitude</a>. </p><p>The term <i>sundial</i> can refer to any device that uses the Sun's <a href="/facts/Horizontal_coordinate_system/msJQPYg0">altitude</a> or <a href="/facts/Azimuth/kEyt9nJ3">azimuth</a> (or both) to show the time. Sundials are valued as decorative objects, <a href="/facts/Metaphor/xwsLaqJI">metaphors</a>, and objects of intrigue and mathematical study. </p><p>The passing of time can be observed by placing a stick in the sand or a nail in a board and placing markers at the edge of a shadow or outlining a shadow at intervals. It is common for inexpensive, mass-produced decorative sundials to have incorrectly aligned gnomons, shadow lengths, and hour-lines, which cannot be adjusted to tell correct time. </p>