The circumference of the Earth around the equator is 40,077 km, and the polar circumference is 40,005 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.