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The speed of light in vacuum, commonly denoted c, is a universal physical constant that is exactly equal to 299,792,458 metres per second (approximately 300,000 kilometres per second; 186,000 miles per second; 671 million miles per hour).
To help compare different orders of magnitude, the following list describes various speed levels between approximately 2.2 × 10 −18 m/s and 3.0 × 10 8 m/s (the speed of light). Values in bold are exact.
The speed of light is 1.8026 × 10 12 furlongs per fortnight (1.8026 terafurlongs per fortnight). By mass–energy equivalence , 1 firkin is equal to 3.249 366 76 × 10 24 firkin· furlong 2 / fortnight 2 (≈ 3.478 × 10 15 BTU , or 3.669 × 10 18 joules ).
The fastest possible speed at which energy or information can travel, according to special relativity, is the speed of light in vacuum c = 299 792 458 metres per second (approximately 1 079 000 000 km/h or 671 000 000 mph). Matter cannot quite reach the speed of light
By timing the eclipses of Jupiter's moon Io, Rømer estimated that light would take about 22 minutes to travel a distance equal to the diameter of Earth's orbit around the Sun. [1] Using modern orbits, this would imply a speed of light of 226,663 kilometres per second, [2] 24.4% lower than the true value of 299,792 km/s. [3]
The two-way speed of light is the average speed of light from one point, such as a source, to a mirror and back again. Because the light starts and finishes in the same place, only one clock is needed to measure the total time; thus, this speed can be experimentally determined independently of any clock synchronization scheme.
Speed; system unit code (alternative) symbol or abbrev. notes sample default conversion combinations SI: metre per second: m/s m/s US spelling: meter per second: 1.0 m/s (3.3 ft/s) m/s ft/s (m/s foot/s) non-SI metric: kilometre per hour: km/h km/h US spelling: kilometer per hour: 1.0 km/h (0.62 mph) km/h mph; Imperial & US customary: mile per ...
At 3 times the speed it was again eclipsed. [3] [4] Given the rotational speed of the wheel and the distance between the wheel and the mirror, Fizeau was able to calculate a value of 2 × 8633m × 720 × 25.2/s = 313,274,304 m/s for the speed of light. Fizeau's value for the speed of light was 4.5% too high. [5] The correct value is 299,792,458 ...