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If a laser is aimed at the earth from behind a satellite, blue light, and it is traveling away at 90% light speed, what spectrum is the light when it reaches the earth?

Quote from: Titanscape on 07/02/2008 02:59:12If a laser is aimed at the earth from behind a satellite, blue light, and it is traveling away at 90% light speed, what spectrum is the light when it reaches the earth? λ' = λSqrt[(1+β)/(1-β)] = λSqrt[(1+0.9)/(1-0.9)] ≈ λ*4.36Blue light has λ > 400 nm then the wavelenght of light arriving on earth is > 400*4.36 ≈ > 1744 nm which is in the infrared.

On the other hand if it is the light that is moving away at 90% the speed of c, then the colour will remain the same.

Yes, the light source is on the satellite, which is traveling away from the earth at 90% light speed. It emits blue light, from a laser. When the light reaches the earth, you have formulated it would be red shifted to infra red? Also how fast would the photons be traveling in relation to the earth?

Quote from: lightarrow on 07/02/2008 08:19:58Quote from: Titanscape on 07/02/2008 02:59:12If a laser is aimed at the earth from behind a satellite, blue light, and it is traveling away at 90% light speed, what spectrum is the light when it reaches the earth? λ' = λSqrt[(1+β)/(1-β)] = λSqrt[(1+0.9)/(1-0.9)] ≈ λ*4.36Blue light has λ > 400 nm then the wavelenght of light arriving on earth is > 400*4.36 ≈ > 1744 nm which is in the infrared.This boy knows his stuff!

the satellite, which is traveling away from the earth at 90% light speed

I get lost with β λ etc. They're all Greek to me []