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The light-second is a unit of length useful in astronomy, telecommunications and relativistic physics.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).
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] [16] [17] 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.
For example, the light-second, useful in astronomy, telecommunications and relativistic physics, is exactly 299 792 458 metres or 1 / 31 557 600 of a light-year. Units such as the light-minute, light-hour and light-day are sometimes used in popular science publications.
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.
15 Pm – 1.59 light-years – possible outer radius of Oort cloud; 20 Pm – 2.11 light-years – maximum extent of influence of the Sun's gravitational field [citation needed] 30.9 Pm – 3.26 light-years – 1 parsec; 39.9 Pm – 4.22 light-years – distance to Proxima Centauri (nearest star to Sun) 81.3 Pm – 8.59 light-years – distance ...
First light, which occurred on November 14, happened as the flight laser transceiver instrument on Psyche received a laser beacon sent from the Optical Communications Telescope Laboratory at NASA ...
In radar-related subjects and in JTIDS, a data mile is a unit of distance equal to 6,000 feet (1,829 metres; 0.9875 nautical miles; 1.136 miles). An international mile is 0.88 data mile. The speed of light is 299,792,458 metres per second (983,571,056 ft/s), or about one foot per nanosecond .
Based on results from the Gaia telescope's second data release from April 2018, an estimated 694 stars will approach the Solar System to less than 5 parsecs in the next 15 million years. Of these, 26 have a good probability to come within 1.0 parsec (3.3 light-years) and another 7 within 0.5 parsecs (1.6 light-years). [3]