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Measuring the speed of light

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Measuring the speed of light

The first real attempt at measuring the speed of light was made by Ole Christensen Rømer in 1676. He was studying Jupiter’s moon Lo motions with a telescope. He observed that Io went round Jupiter once every 42,5 hour when Earth was at it’s closest to Jupiter. When Earth moved away from Jupiter Los its motions took slower than Rømer predicted. The signals from Lo took longer to reach Earth when Jupiter moved away from Earth. The signals from took longer to reach earth when the two planets moved away from each other. This was because of the extra time it took for the light to cross the extra distance. He calculated that it would take about 22 minutes to cross the diameter of Earths orbit.

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Result (km/s)



Olaus Roemer

Jupiter's satellites



James Bradley

Stellar Aberration



Armand Fizeau

Toothed Wheel



Leon Foucault

Rotating Mirror




Albert Michelson

Rotating Mirror


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Albert Michelson

Rotating Mirror




Essen, Gorden-Smith

Cavity Resonator




K. D. Froome

Radio Interferometer




Evanson et al





Adopted Value


As this table shows as time went on, measurements of the speed of light got better and more accurate and precise. This was due to technological advances. The uncertainty of error got les and less.




Britannica Concise Encyclopaedia:

 Publisher: Encyclopaedia Britannica (UK) Ltd; New edition (7 April 2003)

By Dale H. Hoiberg (Editor), Theodore N. Pappas (Editor), Marsha Mackenzie (Editor)

http://math.ucr.edu/home/baez/physics/Relativity/SpeedOfLight/measure_c.html- Original by Philip Gibbs 1997

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