The Noon mark is a type of
sundial that at its simplest is a vertical line on a south facing wall or a north-south line on a horizontal pavement. When the shadow of a point (or a projected image of the Sun) crosses the line it will be midday. Noon in local standard time is defined as when the sun is overhead, however clocks and watches use mean time which varies from standard time by a few minutes each day. The difference is calculated using the
equation of time
In mathematics, an equation is a formula that expresses the equality of two expressions, by connecting them with the equals sign . The word ''equation'' and its cognates in other languages may have subtly different meanings; for example, in F ...
and this can be shown on the noon mark by drawing an
analemma
In astronomy, an analemma (; ) is a diagram showing the position of the Sun in the sky as seen from a fixed location on Earth at the same mean solar time, as that position varies over the course of a year. The diagram will resemble a figure ...
, or using a correction table.
References
Notes
Bibliography
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* Slightly amended reprint of the 1970 translation published by University of Toronto Press (Toronto). The original was published in 1965 under the title ''Les Cadrans solaires'' by Gauthier-Villars (Montrouge, France).
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Sundials
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