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  2. Speed of light - Wikipedia

    en.wikipedia.org/wiki/Speed_of_Light

    For example, in imperial units, the speed of light is approximately 186 282 miles per second, [Note 3] or roughly 1 foot per nanosecond. [ Note 4 ] [ 15 ] [ 16 ] In branches of physics in which c appears often, such as in relativity, it is common to use systems of natural units of measurement or the geometrized unit system where c = 1 .

  3. Light-second - Wikipedia

    en.wikipedia.org/wiki/Light-second

    It is defined as the distance that light travels in free space in one second, and is equal to exactly 299 792 458 m (approximately 983 571 055 ft or 186 282 miles). Just as the second forms the basis for other units of time, the light-second can form the basis for other units of length, ranging from the light-nanosecond (299.8 mm or just under ...

  4. 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.

  5. Gravitational time dilation - Wikipedia

    en.wikipedia.org/wiki/Gravitational_time_dilation

    The speed of light in a locale is always equal to c according to the observer who is there. That is, every infinitesimal region of spacetime may be assigned its own proper time, and the speed of light according to the proper time at that region is always c. This is the case whether or not a given region is occupied by an observer.

  6. Light - Wikipedia

    en.wikipedia.org/wiki/Light

    The speed of light in vacuum is defined to be exactly 299 792 458 m/s (approximately 186,282 miles per second). The fixed value of the speed of light in SI units results from the fact that the metre is now defined in terms of the speed of light. All forms of electromagnetic radiation move at exactly this same speed in vacuum. Different ...

  7. Rømer's determination of the speed of light - Wikipedia

    en.wikipedia.org/wiki/Rømer's_determination_of...

    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]

  8. Galactic year - Wikipedia

    en.wikipedia.org/wiki/Galactic_year

    The Solar System is traveling at an average speed of 230 km/s (828,000 km/h) or 143 mi/s (514,000 mph) within its trajectory around the Galactic Center, [3] a speed at which an object could circumnavigate the Earth's equator in 2 minutes and 54 seconds; that speed corresponds to approximately 1/1300 of the speed of light.

  9. Speed of gravity - Wikipedia

    en.wikipedia.org/wiki/Speed_of_gravity

    metres per second: 299 792 458: Approximate values (to three significant digits) kilometres per hour: 1 080 000 000: miles per second: 186 000: miles per hour [1] 671 000 000: astronomical units per day: 173 [Note 1] parsecs per year: 0.307 [Note 2] Approximate light signal travel times; Distance: Time: one foot: 1.0 ns: one metre: 3.3 ns: from ...