Astronomy difficult question. star velocity

Question

light is gathered from a distant star and one of the spectral lines is obeserved at 540 nm when it should be 400 nm. The velocity of this star is ____km/s

Only enter your numerical answer don't include units. If your answer is negative, be certain to include a minus sign in your answer

Answer 1

Use the approximation for the Doppler shift:

 

Δλ/λ = v/c

 

v = c(Δλ/λ) = (3 x 10⁵ km/s) [( 540 - 400) nm / (400 nm)] 

 

v = 1.05 x 10⁵ km/s