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Redshift calculations

  1. Dec 16, 2008 #1
    [i asked this question in my blog..but i know it would be better answered here]

    what are the calculations of the wave lengths of a cosmological redshift?

    (meaning them all)

    i just wanted to know what precises wavelength determines which red shift..

    thanks guys
  2. jcsd
  3. Dec 16, 2008 #2


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    John Baez has a good link on this.
  4. Dec 17, 2008 #3


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    I'm not sure what it is you want to find out. Do you want to know the various spectral lines of specific chemical elements (like hydrogen alpha line, or sodium yellow, or iron....)?

    The calculation is very simple and is the same for every wavelength---every color.

    The light's wavelength will be increased by a ratio (Z+1) that is the same for all colors and depends only on the time the light was emitted and the time it was received

    The ratio z+1 = (wavelength received)/(wavelength emitted)
    is always equal to the ratio by which the universe expanded during the time that the light was in transit.

    z+1 = (size when light is received)/(size when light was emitted)

    By "size" here I mean a quantity called the scalefactor which tracks the expansion of distances, the expansion of the universe. Think of it as the size of the universe if that were finite and we were able to determine it.
  5. Dec 20, 2008 #4

    oh yeah..i should have been a little more specific..yeah i wanted to know the different spectral lines of each different periodic chemical..

    but what you just said helped..thanks

    any more information..send it my way.

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