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Homework Help: How to calculate relative doppler shift

  1. Mar 10, 2005 #1
    I am to measure the rotational velocity of Io relative to Jupiter, and will do so using a spectrograph.

    I will measure the frequency change of a specific mineral emmision band in the spectra, and then check how much it has shifted from its original wavelenght with a table. Then I use the formula:

    [tex]v = (\Delta \lambda/\lambda) c[/tex]

    where [tex]\Delta \lambda[/tex] is the change of frequency and [tex]\lambda[/tex] is the rest wavelenght. C is speed of light.

    to calculate the velocity for each object.

    The problem is how do I calculate the velocities relative to each other? Io rotates around jupiter, using my method i believe i can only calculate its speed moving relative to earth?
     
    Last edited: Mar 10, 2005
  2. jcsd
  3. Mar 19, 2005 #2

    Andrew Mason

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    Can you not also measure the same emission band for jupiter itself?

    AM
     
  4. Mar 22, 2005 #3
    but the problem is, that I do not know how to integrate the shift of Io relative to jupiter... in order to measure the radial velocity of Io around jupiter, i need to integrate them both into the same forumla in some way :confused:
     
  5. Mar 22, 2005 #4

    Andrew Mason

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    If you measure the Doppler shift from Jupiter itself you would simply subtract/add that from/to the Doppler shifts that you measure from Io.

    AM
     
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