Equatorial circumference of Earth ≈ 40075 km. Speed of light in air ≈ 299700 km/s. Time it takes for light to travel once around the equator ≈ 40075/299700 seconds ≈ 0.1337 seconds. Let me repeat: It takes light *zero point leet* seconds to travel once around the equator.
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As a result of the metre being defined in terms of the speed of light in vacuum, the latter can be expressed as an exact number. When we measure the speed of a car, it is an approximate number due to measurement error. But the speed of light in vacuum is exactly 299792458 m/s.
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Speed of light is not constant

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isn’t it due to be redefined?
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Neglecting relativistic effects?
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The speed of light in a vacuum is constant
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To be more precise, the actual measurement was made with several triangulations on ground between landmarks, starting from Dunkerque and descending through Paris down to Barcelona.
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What will a meter by the end of this year? Maybe a third of the safe distance before a human has a chance of getting infected by the Corona Virus from another human!
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with an error of 0.2 mm in 1 m, caused by a faulty measurement near Barselona.
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