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2. Speed of light - Wikipedia

   en.wikipedia.org/wiki/Speed_of_Light

   For example, for visible light, the refractive index of glass is typically around 1.5, meaning that light in glass travels at ⁠ c / 1.5 ⁠ ≈ 200 000 km/s (124 000 mi/s); the refractive index of air for visible light is about 1.0003, so the speed of light in air is about 90 km/s (56 mi/s) slower than c.

3. Rømer's determination of the speed of light - Wikipedia

   en.wikipedia.org/wiki/Rømer's_determination_of...

   Depending on the value assumed for the astronomical unit, this yields the speed of light as just a little more than 300,000 kilometres per second. The first measurements of the speed of light using completely terrestrial apparatus were published in 1849 by Hippolyte Fizeau (1819–96). Compared to values accepted today, Fizeau's result (about ...

4. Foucault's measurements of the speed of light - Wikipedia

   en.wikipedia.org/wiki/Foucault's_measurements_of...

   In 1845, Arago suggested to Fizeau and Foucault that they attempt to measure the speed of light. Sometime in 1849, however, it appears that the two had a falling out, and they parted ways. [5]: 124 [3] In 1848−49, Fizeau used, not a rotating mirror, but a toothed wheel apparatus to perform an absolute measurement of the speed of light in air.

5. File:Speed of light calculation using Foucault's rotating ...

   en.wikipedia.org/wiki/File:Speed_of_light...

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6. Fizeau's measurement of the speed of light in air - Wikipedia

   en.wikipedia.org/wiki/Fizeau's_measurement_of_the...

   At 3 times the speed it was again eclipsed. [3] [4] Given the rotational speed of the wheel and the distance between the wheel and the mirror, Fizeau was able to calculate a value of 2 × 8633m × 720 × 25.2/s = 313,274,304 m/s for the speed of light. Fizeau's value for the speed of light was 4.5% too high. [5] The correct value is 299,792,458 ...

7. Variable speed of light - Wikipedia

   en.wikipedia.org/wiki/Variable_speed_of_light

   The apparent speed of light will change in a gravity field and, in particular, go to zero at an event horizon as viewed by a distant observer. [4] In deriving the gravitational redshift due to a spherically symmetric massive body, a radial speed of light dr / dt can be defined in Schwarzschild coordinates , with t being the time recorded on a ...

8. Light - Wikipedia

   en.wikipedia.org/wiki/Light

   The speed of light in vacuum is defined to be exactly 299 792 458 m/s (approximately 186,282 miles per second). The fixed value of the speed of light in SI units results from the fact that the metre is now defined in terms of the speed of light. All forms of electromagnetic radiation move at exactly this same speed in vacuum.

9. Velocity factor - Wikipedia

   en.wikipedia.org/wiki/Velocity_factor

   The velocity factor (VF), [1] also called wave propagation (relative) speed or (relative) velocity of propagation (VoP or ), [2] of a transmission medium is the ratio of the speed at which a wavefront (of an electromagnetic signal, a radio signal, a light pulse in an optical fibre or a change of the electrical voltage on a copper wire) passes through the medium, to the speed of light in vacuum.