Light travels fast. It can travel 300,000 km per second. This speed is fast enough to go around the world seven and a half times in just a second.
It was around 17th century when there were a number of views about the nature of light. There were several scientists like Pierre Gassendi and Rene Descartes, who explained the behavior of light. Below are the lists of scientists who contributed in determining the speed of light and how each was able to come up with these discoveries.
a.) Ole Rømer (1670)
A Danish scientist who went to the observatory in Paris to observe the eclipses of Io, one of Jupiter's moons. He discovered that the speed of light is finite by measuring the apparent changes in the revolution of Io. With this, he claimed that it took 22 minutes for the light to travel across the diameter of the Earth's orbit. If we know the diameter of the orbit, then we can get the speed of the light. However, it was unknown in his time so he was not able to work it. He still presented his findings and as expected, many were skeptical about it.
b.) James Bradley (1727)
An English scientist who also used astronomical methods, like Rømer, to determine the speed of light. In his studies, he examined the position of stars which is known as the concept of stellar aberration. He inferred that the light is traveling towards the earth but the earth is moving at the same time so we get a difference in where the star is supposed to be to where the star is seemed to be. He was then able to determine the speed of light considering that the earth's speed has a particular value. He concluded that the speed of light is around 303,000 km per second.
c.) Hippolyte Louis Fizeau
He used mirrors and cogwheel in his experiment to determine the speed of light. The half silver deer were served as the light source. The light would pass through the half-silvered mirror and the spinning cogwheel then strikes the other mirror. The light would return via the separation of the cog and then it would go off the side halves of the mirror. Because the cogwheel is spinning, the light would pass through the gap and get blocked by the time the light returns. He calculated the speed by considering multiplying the distance twice (reflected) divided time it takes which is also multiplied twice. He also considered the cog with exactly 720 teeth. He then concluded that the speed of light is 313,000 km per second. His experiment was the first wheel to determine the speed of light without using astronomical methods referred to as time of flight methodology. However, still, it was not accurate.
d.) Jean Bernard Léon Foucault
He improved Fizeau's experiment by replacing the cogwheel with a rotating mirror and reducing the length of the path. As the mirror spins, the light travels down through the half-silvered mirror and reflects again at a different angle depending on the frequency of the speed. He determined the speed of light by considering the angle between the light source number of spins and path length. He calculated the speed of light to reach 298,000 km per second.
Among the four scientists mentioned above, it was Foucault's which is closer to the speed of light we have today.
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