Who, when and how does the speed of light work out? Who knows?

Who, when and how does the speed of light work out? Who knows?

Romer's satellite eclipse
The time between two successive satellite eclipses should be exactly the same, but when the earth moves away from Jupiter, the satellite eclipses are longer than when the earth moves towards Jupiter. Romer explains this phenomenon by using the limited propagation speed of light, When the earth moves away from Jupiter, light must catch up with the earth. Therefore, the time between the two eclipses observed from the ground is longer than the actual time. When the earth moves towards Jupiter, the time is shorter, At that time, the observation was carried out continuously throughout the year. Romer calculated the speed of light by observing the time variation of satellite eclipse and the diameter of earth's orbit. Because only the approximate value of earth's orbit radius was known at that time, the calculated speed of light was only 214300km / s, But it is the first record in the history of measuring the speed of light. Later, the time of Jupiter's eclipse was measured by photographic method. After the accuracy of measuring the radius of the earth's orbit was improved, the speed of light obtained by Romer method was 299840 ± 60km / s
This is the first time (scientific) to measure the speed of light. The earlier one was measured by Galileo, which is too unreliable to ignore
The experimental method for measuring the speed of light was first carried out by Fizeau in 1849. He used the method of regularly blocking light (rotating gear method) for automatic recording. The schematic diagram of the experiment is as follows. The light from the light source s passes through the converging lens L1 to the semi silvered mirror a, and then converges in the gap between the teeth a and a 'of the gear W, and then passes through the lens L2 and L3 to reach the mirror M, If the gear is rotated, the gear will turn an angle within the time △ t after the light reaches the M mirror and then reflects back. If the gap between a and a 'is occupied by a tooth (or a'), the reflected light will be blocked, However, if the gear turns to such an angle that the light reflected by the M mirror passes through the gap between the other teeth, the observer will see the light again. When the gear turns faster and the reflected light is blocked by the other tooth, the light disappears again. Thus, when the speed of the gear gradually increases from zero, The speed of light C = 4nvl can be deduced from the rotation speed V of the gear, the number of teeth N and the distance L between the gear and m
In Fizeau's experiment, when a gear with 720 teeth rotates 12.67 times in a second, the light will be blocked for the first time and disappear. The time required for the gap to alternate with the teeth is 1 / 12.67 s
In this time, the light path is 2 × 8633 meters, so the light speed c = 2 × 8633 × 18244 (M / s) ≈ 315 × 108 (km / s)
In addition to the rotating gear method, Kerr box method is also used in modern times. In 1941, Anderson measured C = 299776 ± 6km / s by Kerr box method, and in 1951, bergsgland measured C = 299793.1 ± 0.3km/s by Kerr box method