Chinese sundial of the Eastern Han dynasty (2nd century CE). Hemispherical Greek sundial from Ai Khanoum, Afghanistan (3rd–2nd century BCE). The heritage of sundials was recognised and sundial societies were set up worldwide, and certain legislations made studying sundials part of their national school curriculums. Affordable scientific calculators made the algebraic methods as accessible as the geometric constructions- and the use of computers made dial plate design trivial. No longer utilitarian, sundials remained as popular ornaments, and several popular books promoted that interest- and gave constructional details. The use of logarithms allowed algebraic methods of laying out dials to be employed and studied. In the late nineteenth century sundials became objects of academic interest. Dials were laid out using straightedges and compasses. A clock and a sundial were used together to measure longitude. After the invention of the clock, the sundial maintained its importance, as clocks needed to be reset regularly from a sundial, because the accuracy of early clocks was poor. Before the invention of the clock the sundial was the only source of time. Before the coming of the railways in the 1840s, local time was displayed on a sundial and was used by the government and commerce. Sundials have been invented independently in every major culture and became more accurate and sophisticated as the culture developed. Both the azimuth (direction) and the altitude (height) can be used to create time measuring devices. As the Earth turns on its polar axis, the sun appears to cross the sky from east to west, rising at sun-rise from beneath the horizon to a zenith at mid-day and falling again behind the horizon at sunset. Ī sundial is a device that indicates time by using a light spot or shadow cast by the position of the Sun on a reference scale. World's oldest known sundial, from Egypt's Valley of the Kings (c.
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