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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).
By combining many such measurements, a best fit value for the light time per unit distance could be obtained. For example, in 2009, the best estimate, as approved by the International Astronomical Union (IAU), was: [102] [103] light time for unit distance: t au = 499.004 783 836 (10) s, c = 0.002 003 988 804 10 (4) AU/s = 173.144 632 674 (3) AU/d.
The amount of time light takes to travel one fermi (about the size of a nucleon) in a vacuum. zeptosecond: 10 −21 s: One sextillionth of a second. Time measurement scale of the NIST and JILA strontium atomic clock. Smallest fragment of time currently measurable is 247 zeptoseconds. [3] attosecond: 10 −18 s: One quintillionth of a second ...
Light-second: 0.002 – Distance light travels in one second – Lunar distance: 0.0026 – Average distance from Earth (which the Apollo missions took about 3 days to travel) – Solar radius: 0.005 – Radius of the Sun (695 500 km, 432 450 mi, a hundred times the radius of Earth or ten times the average radius of Jupiter) – Light-minute: 0 ...
Clock time and calendar time have duodecimal or sexagesimal orders of magnitude rather than decimal, e.g., a year is 12 months, and a minute is 60 seconds. The smallest meaningful increment of time is the Planck time―the time light takes to traverse the Planck distance, many decimal orders of magnitude smaller than a second. [1]
The Planck time, denoted t P, is defined as: = = This is the time required for light to travel a distance of 1 Planck length in vacuum, which is a time interval of approximately 5.39 × 10 −44 s. No current physical theory can describe timescales shorter than the Planck time, such as the earliest events after the Big Bang. [ 30 ]
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The speed of light in IAU is the defined value c 0 = 299 792 458 m/s of the SI units. In terms of this speed, the old definition of the astronomical unit of length had the accepted value: [3] 1 au = c 0 τ A = (149 597 870 700 ± 3) m, where τ A is the transit time of light across the astronomical