Question

The spectral line for a given element, received from a distant star is shifted towards the longer wavelength by 0.028% . What is the velocity of the star?​

Answer 1

It is given that, The spectral line for a given element, received from a distant star is shifted towards the longer wavelength by 0.028% .

i.e., $\frac{\Delta\lambda}{\lambda}\times100=0.028\%$

Since, the wavelength of light from a star is shifting towards longer wavelength side, then ∆λ is positive, hence star is moving away from the earth, it means , v will be negative in sign. and it can be found by,

v =- $\frac{\Delta\lambda}{\lambda}c$

= -0.028/100 × 3× 10^8 m/s

= -84 × 10³ m/s

= -8.4 × 10⁴ m/s