How do you differentiate between redshift and blueshift in the Doppler effect?

Redshift and blueshift in the Doppler effect are differentiated by the movement of the source relative to the observer.

In the Doppler effect, the change in frequency or wavelength of a wave for an observer moving relative to the source of the wave is observed. This effect is commonly observed with sound waves, but it also applies to light waves, and it is in this context that we discuss redshift and blueshift.

Redshift occurs when the source of light is moving away from the observer. This causes the light waves to stretch out, increasing their wavelength and shifting the light towards the red end of the spectrum, hence the term 'redshift'. This is because red light has a longer wavelength than other colours in the visible spectrum. Redshift is often observed in astronomy, where distant galaxies are moving away from us due to the expansion of the universe. This results in their light being redshifted and allows astronomers to estimate how fast these galaxies are moving away from us.

On the other hand, blueshift occurs when the source of light is moving towards the observer. This causes the light waves to compress, decreasing their wavelength and shifting the light towards the blue end of the spectrum, hence the term 'blueshift'. Blue light has a shorter wavelength than other colours in the visible spectrum. Blueshift is also observed in astronomy, for example when a star is moving towards us, its light appears more blue than it would if the star were stationary.

In summary, the key difference between redshift and blueshift in the Doppler effect is the direction of the movement of the light source relative to the observer. If the source is moving away, the light is redshifted, and if the source is moving towards the observer, the light is blueshifted. This change in colour is due to the change in wavelength of the light, with longer wavelengths appearing red and shorter wavelengths appearing blue.