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Homework Help: Minimum and Maximum Observed Frequencies?

  1. Oct 4, 2015 #1
    1. The problem statement, all variables and given/known data
    Let's say you want to find the minimum and maximum observed frequencies of light observed on Earth from the sun, when considering the Earth's motion around the sun. How would you go about doing this if you assume Earth takes time X to complete a revolution around radius R?

    2. Relevant equations
    Well, this is an example of Doppler Shift I assume, so
    frequency observed = Vphase / [ (Vsource + Vphase)(frequency node)]
    where Vphase is the speed of light.

    3. The attempt at a solution
    So frequency observed is easy enough to set up, but how I'm not sure how to incorporate the parameters X and R to get the minimum and maximum frequencies.
  2. jcsd
  3. Oct 4, 2015 #2


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    Staff: Mentor

    The question kind of doesn't make any sense to me. Is that the exact wording of the problem statement that you have been given?

    The max and min frequencies of "observed" light from the Sun would depend on human vision, no? Or do you mean observed some other way? And if some other way, it seems the max and min range would be quite wide.

    Also, the problem seems to be implying that you should use a circular radius of "R". If the radius is circular, there will be no Doppler shift. And if you use the real elliptical orbit of the Earth around the Sun and get some Doppler shift, there is no "radius R"...
  4. Oct 4, 2015 #3
    So basically imagine you are observing an object in space with a telescope and it is moving away from the sun.

    More specifically, the question states that: you are observing a source that is on the y-z plane, the sun is on the origin and the Earth is moving around the sun. The source is moving away from the sun along the z-axis with velocity Vsource. The question asks to find the minimum and maximum observed frequencies of that source from the Earth. Vphase is the speed of light c and the Earth takes X time to move around the sun in radius R.

    I hope that makes more sense.
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