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How fast does light travel?

The speed of light
  • Light travels through the vacuum of space at 299,793 km per second (which is 1,079,252,960 km per hour); or 186,282 miles per second (which is 670,619,880 miles per hour).
  • The speed of light is not constant; it travels about 3 percent more slowly through air and much more slowly through glass or water.

Some examples of different mediums and their respective index;

  • Air/Vacuum with an index of 1.0 which is 299,460 km/sec
  • Water with an index of 1.33 which is 225,158 km/sec
  • Glass with an index of 1.5 which is 199,640 km/sec
  • Diamond with an index of 2.42 which is 123,744 km/sec

Estimated travel time of light between places or objects

  • Sun to Earth: 8.3 minutes
  • Moon to Earth: 1.25 seconds 
  • Sun to Pluto: 5 hours and 40 minutes
  • Pluto to the nearest star: 4.3 years
  • Across our Milky Way Galaxy: 100 000 years
  • Andromeda Galaxy to Earth: 2.5 million years
  • 1 Kilometer: 3.3 microseconds
  • 1 meter: 3.3 nanoseconds 
  • Circumference of the earth ( measured on the equator ): 134 milliseconds  
  • Alpha Centauri to earth : 4.4 years
  • Sun to Jupiter: 41 minutes
  • Sun t Saturn: 1 hour and 25 minutes
  • Sun to Neptune: 4.2 hours
  • Sun to Acrux ( Brightest star of Southern Cross): 321 years
  • Sun to Crab Nebula: 6300 years
  • Earth to known limit of observable Universe: 15,000,000,000 years
  • Amount of times around the earth in 10 seconds: Approx: 70 times

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