This is a question about speed of light I need some help please. Thanks/!?!

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1 Answer
Dec 26, 2017

Yay! History of science :) Just need to start with knowing that Aristotle had assumed (or declared?) the speed of light to be infinite.

Explanation:

The original measurement (as far as I know) was by Galileo who took two lamps onto hills either side of the town where he was living. Galileo planned to start his “clock” show the first lamp, an assistant on seeing this would expose his lamp. On seeing the second lamp flash, Galileo would stop the clock. As you might imagine he measured 2 x human reaction time quite accurately!

Then came a really clever deduction from an unexpected direction. Roemer was looking at the visible moons around Jupiter in 1675 when he noticed that they deviated from the published times for occultation (hiding) and appearance (the eclipses) behind Jupiter by predictable amounts that varied over a 12 month cycle. He deduced it was due to the earth’s rotation around the Sun meaning that the extra distance between earth and Jupiter could be measured in terms of light’s ‘flight time’.

He got a value of around 200 000 km/s, but this was improved on by others using his technique with a better value for the sun-earth distance.

The next serious attempt was made by Fizeau in the late 1840’s who used a toothed gear with a very fine beam of light shining between the teeth, it then bounced off a mirror, before returning towards the gear wheel. The light would just be obscured when the gear wheel was rotating quickly enough to turn to place the next tooth of the gear wheel in the path of the light as it was returning. His value for the speed of light was 315 000 km/s (within about 5% of the modern value.)

Finally, Foucault improved on Fizeau’s method a few years later by using a rotating mirror to get a value of around 299 000 km/s - very close indeed to the currently accepted value of 299 979 km/s.

Hope this is ok, might required some editing!