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  2. Speed of light - Wikipedia

    en.wikipedia.org/wiki/Speed_of_Light

    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).

  3. FFF system - Wikipedia

    en.wikipedia.org/wiki/FFF_system

    FFF system. The furlong–firkin–fortnight (FFF) system is a humorous system of units based on unusual or impractical measurements. The length unit of the system is the furlong, the mass unit is the mass of a firkin of water, and the time unit is the fortnight. [1][2] Like the SI or metre–kilogram–second systems, there are derived units ...

  4. Data mile - Wikipedia

    en.wikipedia.org/wiki/Data_mile

    In radar -related subjects and in JTIDS, a data mile is a unit of distance equal to 6000 feet (1.8288 kilometres or 0.987 nautical miles). An international mile is exactly 0.88 of a data mile. The speed of light is 983571056 ft/s, or about one foot per nanosecond. If it were exactly one foot per nanosecond, and a target was one data mile away ...

  5. Light-year - Wikipedia

    en.wikipedia.org/wiki/Light-year

    The product of Simon Newcomb's J1900.0 mean tropical year of 31 556 925.9747 ephemeris seconds and a speed of light of 299 792.5 km/s produced a light-year of 9.460 530 × 10 15 m (rounded to the seven significant digits in the speed of light) found in several modern sources [10] [11] [12] was probably derived from an old source such as C. W ...

  6. Space travel under constant acceleration - Wikipedia

    en.wikipedia.org/wiki/Space_travel_under...

    From the planetary frame of reference, the ship's speed will appear to be limited by the speed of light — it can approach the speed of light, but never reach it. If a ship is using 1 g constant acceleration, it will appear to get near the speed of light in about a year, and have traveled about half a light year in distance. For the middle of ...

  7. Foucault's measurements of the speed of light - Wikipedia

    en.wikipedia.org/wiki/Foucault's_measurements_of...

    He used carefully calibrated tuning forks to monitor the rotation rate of the air-turbine-powered mirror R, and he would typically measure displacements of the slit image on the order of 115 mm. [7] His 1879 figure for the speed of light, 299944±51 km/s, was within about 0.05% of the modern value.

  8. Time dilation - Wikipedia

    en.wikipedia.org/wiki/Time_dilation

    The faster the relative velocity, the greater the time dilation between them, with time slowing to a stop as one clock approaches the speed of light (299,792,458 m/s). In theory, time dilation would make it possible for passengers in a fast-moving vehicle to advance into the future in a short period of their own time.

  9. Astronomical unit - Wikipedia

    en.wikipedia.org/wiki/Astronomical_unit

    (The reason for the change was an improved method of measuring the speed of light.) The speed of light could then be expressed exactly as c 0 = 299,792,458 m/s, a standard also adopted by the IERS numerical standards. [19] From this definition and the 2009 IAU standard, the time for light to traverse an astronomical unit is found to be τ A ...