Applications of Doppler effect
Doppler effect has many applications. Specifically Doppler effect in light has many applications in astronomy.
As an example, while observing the spectra from distant objects like stars or galaxies, it is possible to determine the velocities at which distant objects like stars or galaxies move towards or away from Earth. If the spectral lines of the star are found to shift towards red end of the spectrum (called as red shift) then the star is receding away from the Earth. Similarly, if the spectral lines of the star are found to shift towards the blue end of the spectrum (called as blue shift) then the star is approaching Earth.
Let ∆λ be the Doppler shift. Then ∆λ= v/c λ, where v is the velocity of the star. It may be noted that Doppler shift measures only the radial component (along the line of sight) of the relative velocity v.