Time has long been an important subject of study in religion, philosophy, and science, but defining it in a manner applicable to all fields without circularity has consistently eluded scholars.
Nevertheless, diverse fields such as business, industry, sports, the sciences, and the performing arts all incorporate some notion of time into their respective measuring systems.
Time in physics is unambiguously operationally defined as "what a clock reads". See Units of Time. Time is one of the seven fundamental physical quantities in both the International System of Units and International System of Quantities. Time is used to define other quantities – such as velocity – so defining time in terms of such quantities would result in circularity of definition. An operational definition of time, wherein one says that observing a certain number of repetitions of one or another standard cyclical event (such as the passage of a free-swinging pendulum) constitutes one standard unit such as the second, is highly useful in the conduct of both advanced experiments and everyday affairs of life. The operational definition leaves aside the question whether there is something called time, apart from the counting activity just mentioned, that flows and that can be measured. Investigations of a single continuum called spacetime bring questions about space into questions about time, questions that have their roots in the works of early students of natural philosophy.
Temporal measurement has occupied scientists and technologists, and was a prime motivation in navigation and astronomy. Periodic events and periodic motion have long served as standards for units of time. Examples include the apparent motion of the sun across the sky, the phases of the moon, the swing of a pendulum, and the beat of a heart. Currently, the international unit of time, the second, is defined by measuring the electronic transitionfrequency of caesium atoms (see below). Time is also of significant social importance, having economic value ("time is money") as well as personal value, due to an awareness of the limited time in each day and in human life spans.
A chronometer watch is a watch tested and certified to meet certain precision standards. In Switzerland, only timepieces certified by the COSC may use the word 'Chronometer' on them. However, numerous prominent Swiss watch manufacturers do not submit their movements for COSC certification, although such movements would probably easily qualify as chronometers under the COSC certification rules.
The term chronometer is also used to describe a marine chronometer used for celestial navigation. The marine chronometer was invented by John Harrison in 1730. This was the first iteration of a series of chronometers which enabled accurate marine navigation. For the next 250 years, an accurate chronometer was essential to any kind of marine or air navigation until the implementation of global satellite navigation at the end of the 20th century. The marine chronometer is no longer used for navigation.
Bede (also Saint Bede, the Venerable Bede, or (from Latin) Beda) (c. 672 or 673 – May 25, 735), was a Benedictinemonk... He is well known as an author and scholar, and his most famous work, Historia ecclesiastica gentis Anglorum (The Ecclesiastical History of the English People) gained him the title "The father of English history"... His work On the Reckoning of Time (De temporum ratione) included an introduction to the traditional ancient and medieval view of the cosmos, including an explanation of how the spherical earth influenced the changing length of daylight, of how the seasonal motion of the Sun and Moon influenced the changing appearance of the New Moon at evening twilight, and a quantitative relation between the changes of the Tides at a given place and the daily motion of the moon.
... that merkhets were Ancient Egyptian timekeeping devices that tracked the movement of certain stars over the meridian in order to ascertain the time during the night, when sundials could not function?
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