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History of sundials. World's oldest known sundial, from Egypt's Valley of the Kings (c. 1500 BC), used to measure work hours. [ 1][ 2][ 3] A 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. [ 4] As the Earth turns on its polar axis, the sun appears to cross the sky ...
A sundial is a horological device that tells the time of day (referred to as civil time in modern usage) when direct sunlight shines by the apparent position of the Sun in the sky. In the narrowest sense of the word, it consists of a flat plate (the dial) and a gnomon, which casts a shadow onto the dial.
History of timekeeping devices. A marine sandglass. It is related to the hourglass, nowadays often used symbolically to represent the concept of time. The history of timekeeping devices dates back to when ancient civilizations first observed astronomical bodies as they moved across the sky. Devices and methods for keeping time have gradually ...
Roman timekeeping. In Roman timekeeping, a day was divided into periods according to the available technology. Initially, the day was divided into two parts: the ante meridiem (before noon) and the post meridiem (after noon). With the introduction of the Greek sundial to Rome from the Samnites circa 293 BC, the period of the natural day from ...
More complex devices were developed over time, the earliest surviving one is a limestone sundial that dates back to 1500 BCE, discovered in the Valley of the Kings in 2013. [3] It was found in a housing area of construction workers and its division of daytime into 12 parts was possibly used to measure work hours. [3]
A moment ( momentum) is a medieval unit of time. The movement of a shadow on a sundial covered 40 moments in a solar hour, a twelfth of the period between sunrise and sunset. The length of a solar hour depended on the length of the day, which, in turn, varied with the season. [ 1] Although the length of a moment in modern seconds was therefore ...
Chronometry. Chronometry[ a] or horology[ b] ( lit. 'the study of time') is the science studying the measurement of time and timekeeping. [ 3] Chronometry enables the establishment of standard measurements of time, which have applications in a broad range of social and scientific areas. Horology usually refers specifically to the study of ...
Sundials can be horizontal, vertical, or in other orientations. Sundials were widely used in ancient times. [9] With knowledge of latitude, a well-constructed sundial can measure local solar time with reasonable accuracy, within a minute or two. Sundials continued to be used to monitor the performance of clocks until the 1830s, when the use of ...