At an astronomical conference, an astronomer gives a report on a star that interests astronomers because of hints that it may have a planet around it. In his report the astronomer gives the average speed with which this star is moving away from the Sun. How did the astronomer measure this speed?

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.

waves moving from a fast medium to a slow medium will experience a reflection as light travels more slowly than red light. total internal reflection occurs when the critical angle is.