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nHowndo you measure the fastest thing known in the universe?
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nFizeau,na French physicist who was born on this date in 1819, was the firstnperson to successfully (although approximately) measure the speed ofnlight without using astronomical calculations. How did he do it?
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nFizeaunsent a narrow beam of light between gear teeth on the edge of anrotating wheel. The beam of light traveled 8 kilometers (about 5nmiles) to a mirror and then bounced back to the wheel. If the spinnwas fast enough, a tooth would block the light. Because Fizeau knewnthe rotational speed of the wheel and the mirror’s distance, Fizeaunwas able to directly measure that light travels 299,792,458 metersnper second (approximately 186,000 miles per second). Actually, thatnis the speed of light in a vacuum (no air or other material). Lightntravels slightly slower in air—ONLY 299,792,368 meters pernsecond—and slightly slower yet through glass or water. Fizeau’snmeasurements were good enough to show the difference between lightntraveling in air and in water.
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nnFizeau also made discoveries aboutnpolarization of light, the expansion of crystals, the Doppler effect,nand even daguerreotypes (early photography).