Answer:
Explanation:
The astronomer must have evaluated the Doppler shift in the lines of star's spectrum. The speed at which the star is moving away from the sun will cause in the shift in spectral lines emitted from the star. The shift in spectral line is not a change of whole pattern but a change is shade of color. It may get bluish or reddish in nature. So if the star moves away the spectral lines converge to a more reddish color. The degree of convergence is calibrated with respect to speed of light c = 3.0 * 10^8 m/s.