B How to calculate the Doppler Shift Frequency

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1. May 30, 2017

mpolo

I would like to know the formula for calculating the Doppler shifted frequency received by someone on Earth that is received from a space ship traveling at 85 percent the speed of light away from Earth. Please show example of the formula being used. Lets say the spacecraft sent a radio signal from the ship at 100 MHZ what would the received frequency of that signal be on earth?

2. May 30, 2017

PeroK

Have you tried googling for "relativistic Doppler shift"?

3. May 30, 2017

mpolo

Yes I have looked but I would like to see someone actually do it with real numbers and a bit of explanation I am curious as to how the time dilation works in the scheme of things. In other words what would it look like if I were in a space ship traveling at 99% the speed of light towards a group of stars. Would the light of the stars be blue shifted? If so, by how much?

Last edited: May 30, 2017
4. May 30, 2017

PeroK

The equation is:

$f_o = f_s \sqrt{\frac{1+v}{1-v}}$

Where $f_o=$ is the observed frequency, $f_s$ the frequency of the source and $v$ is the speed expressed as a fraction of the speed of light. E.g. $v = -0.85$ or $v = 0.99$ in the two examples you wanted. If $v$ is positive then motion of the source is towards the observer and if $v$ is negative then motion of the source is away from the observer.

You could put that formula into a calculator or spreadsheet and plug away!

5. May 30, 2017

mpolo

Oh Man, Thanks this is perfect thanks so much! This is exactly what I was looking for! Going to have fun putting this is to a program and trying different values.