1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Homework Help: Doppler Shift and Astronomy

  1. Jul 13, 2014 #1
    1. The problem statement, all variables and given/known data

    The Sun rotates with a period of 24.7 days and has a radius of 7.00 x 108 m. For a terrestrial observer, Calculate the resultant Doppler shift of light of wavelength 500 nm which is emitted from the solar equator at :

    i)each side of the disc,
    ii)the center of the solar disc

    The speed of light, c = 3.00 x 108 m/s

    2. Relevant equations

    wavelength shift Δλ = v/c λ

    v : speed of of the source
    c: speed of light
    λ : wavelength of source

    speed = distance/ time

    24.7 days = 2134080 s

    500 nm = 5.0 x 10-7 m

    Circumference of a circle = 2∏r = 4.4 x 109 m

    3. The attempt at a solution

    i) I first found the speed of the source, v

    speed = 4.4 x 109 m / 2134080 s
    = 2060.9 m/s

    using the equation for wavelength shift, plug in values

    Δλ = (2060.9 / 3.00 x 108 m/s ) 5.0 x 10-7 m

    = 3.43 x 10-12 m
    = 0.00343 nm

    ii) i assumed that λ = 0

    therefore Δλ = (328 / 3.00 x 108 m/s ) 0
    = 0 m

    .. not sure if my workings are correct ....thanks for any help
    1. The problem statement, all variables and given/known data

    2. Relevant equations

    3. The attempt at a solution
    Last edited: Jul 14, 2014
  2. jcsd
  3. Jul 14, 2014 #2

    rude man

    User Avatar
    Homework Helper
    Gold Member

    Why λ = 0 at the center?

    Where did 328 come from? This is roughly the average speed of the cg's of the Earth from the Sun. But if you include that speed you have to include it in part (i) also. So the doppler shift from one side of the sun's disc will be different than that from the other and will depend on the time of year.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted