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Measuring the speed of light

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Introduction

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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Middle

Date

Author

Method

Result (km/s)

Error

1676

Olaus Roemer

Jupiter's satellites

214,000

1726

James Bradley

Stellar Aberration

301,000

1849

Armand Fizeau

Toothed Wheel

315,000

1862

Leon Foucault

Rotating Mirror

298,000

+-500

1879

Albert Michelson

Rotating Mirror

299,910

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Conclusion

rowspan="1">

1926

Albert Michelson

Rotating Mirror

299,796

+-4

1947

Essen, Gorden-Smith

Cavity Resonator

299,792

+-3

1958

K. D. Froome

Radio Interferometer

299,792.5

+-0.1

1973

Evanson et al

Lasers

299,792.4574

+-0.001

1983

Adopted Value

299,792.458

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.

Bibliography

http://galileoandeinstein.physics.virginia.edu/lectures/spedlite.html

http://schools-wikipedia.org/wp/s/Speed_of_light.htm

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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