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Hello, I've read it takes 1/7 of a second for light to travel around the world. I would like to know how the scientists came to this conclusion.
Answer 1:

The circumference of the Earth around the equator is 40077 km, and the polar circumference is 40005 km. We could round this to 40 000 km or 40 000 000 m.
The speed of light is 299 792 458 m / sec in vacuum.
This means the light travels 299 792 458 m in 1 sec
and it will take for 40 000 000 m about 1/7 of a sec, since light will be a little bit slower in air than it is in vacuum.


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