A sundial or dial is an instrument for showing the hour of the day from the shadow thrown while the sun is shining by a stile or gnomon upon a graduated surface. The sundial has been known from the earliest times amongst Egyptians, Chaldeans, and Hebrews. From those eastern nations it came to the Greeks. It was introduced into Rome during the first Punic war.
Sundials are of various construction, horizontal, inclined, or upright, the principle in every case being to show the sun's distance from the meridian by means of the shadow cast by the stile or gnomon. The stile is made parallel with the earth's axis,and may be considered as coinciding with the axis of the diurnal rotation. Consequently as the sun moves westwards the shadow of the stile moves round in the opposite direction, falling on the meridian lines so marked as to represent the hours of the day. The sundial of course gives solar time, which, except on four days of the year, is slightly different from that of a well-regulated clock. Since at least 1900 sundials have been rather articles of curiosity or ornament than of use. Research Sundial
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Abbreviations
General Information
Research Sundial
