The History of Keeping Time - Karen Mensing
View full lesson: http://ed.ted.com/lessons/the-history-of-keeping-time Where did time-telling come from? What are time zones and why are there so many of ...
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We check the time every day, all day long. But did you ever wonder - where did telling time come from? Why does it matter what time it is? Who determined the clock and why in the world are there so many different time zones? The first form of telling time was the sundial and the earliest sundials known from the archaeological record are obelisks from nearly 5,000 years ago. Sundials indicate the time by casting a shadow onto a surface. The object that casts the shadow is a stick in the center known as a gnomon. A well-constructed sundial can measure time with remarkable accuracy, and sundials were used to monitor the performance of clocks until the modern era. But sundials have their limitations too. Obviously they require the sun to shine, so they don't work at all during the nigh...
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We check the time every day, all day long. But did you ever wonder - where did telling time come from? Why does it matter what time it is? Who determined the clock and why in the world are there so many different time zones? The first form of telling time was the sundial and the earliest sundials known from the archaeological record are obelisks from nearly 5,000 years ago. Sundials indicate the time by casting a shadow onto a surface. The object that casts the shadow is a stick in the center known as a gnomon. A well-constructed sundial can measure time with remarkable accuracy, and sundials were used to monitor the performance of clocks until the modern era. But sundials have their limitations too. Obviously they require the sun to shine, so they don't work at all during the nigh...
