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Light second

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The light second is the distance that the light travels in vacuum in one second and so is a unit of distance.

Similar units are the light minute, light hour, light day, light week, light month, light year.

Numerical value

As opposed to the light year, whose value more or less depends on the definition of year, the value of the light second is defined exactly.

Comparison to other Units

  • 1 AU = 499 light seconds
  • 1 light second = 299,792.458 km
  • 1 light second = 186,282.397 mi[2]
  • 1 light second = 983,571,056.4 ft[3]
  • 1 light second = 327,857,018.8 yd[4]

Distances in Light Seconds

  • the maximum distance between earth and moon is about 1.3 light seconds
  • the maximum distance between earth and sun is about 499 light seconds or 8.3 light minutes


  1. Review of Particle Physics Particle Data Group: W.-M. Yao et al., J. Phys. G 33, 1 (2006).
  2. 1 mi = 1609.344 m
  3. 1 ft = 0.3048 m
  4. 1 yd = 0.9144 m