Doppler Effect

The phenomenon of changing the frequency or wavelength of a wave in relation to an observer who is moving relative to the wave source is called the Doppler effect. This effect can be observed in sound waves, light waves, and other types of waves.

Doppler Effect in Light Waves

When a star is moving towards earth, the light waves emitted by the star are compressed or squeezed. This compression results in a shift of the lines towards the blue end of the spectrum. This shift is called the blue shift.

Explanation

The light waves emitted by a star have a certain frequency and wavelength. When the star moves towards the earth, the distance between the source of the light waves and the observer decreases. This results in a compression of the light waves, which increases the frequency of the wave. The increase in frequency results in a shift towards the blue end of the spectrum.

The blue shift is observed in the spectral lines of the star. These spectral lines are dark lines that are observed when the light from the star is passed through a prism or a diffraction grating. These lines are produced by the absorption of certain frequencies of light by the gases in the outer layers of the star.

The blue shift is an indication that the star is moving towards the observer. The amount of blue shift is proportional to the speed of the star relative to the observer.

Conclusion

When a star is moving towards the earth, the spectral lines are shifted towards the blue end of the spectrum. This shift is called the blue shift and is a result of the Doppler effect. The blue shift is an indication that the star is moving towards the observer.