Does Light Always Move At The Same Speed?


How fast can you run?





10 Km/h, 20 Km/h ....or faster?





Imagine the fastest speed that can be achieved in space?





it's 300000 Km/h, the speed of light.





No matter how far away we look into the distant Universe, the physics governing atoms, and therefore... our definitions of length, time, and the speed of light, are exactly the same.
Source: NASA Web




  1. Light, no matter how high-or-low in energy, always moves at the speed of light, so long as it's traveling through the vacuum of empty space.
  2. By passing that light into a non-vacuum medium, you can change its speed so long as it's in that medium.
  3. Light of different energy will change its speed by slightly different amounts, depending on the properties of that medium.
  4. Once you leave that medium and go back into a vacuum again, that light goes back to moving at the speed of light.




Why Is the Sky Blue? | NASA Space Place – NASA Science for Kids
Source: NCERT Book