What is the red shift?

Hint: Red shift shows that when the objects come closer or move away from us, then light also gets shifted to shorter or longer wavelengths. As the name suggests, in redshift, the light gets shifted towards the red part of the spectrum.

Complete step by step solution:
Step I:
Whenever there is change in the frequency or wavelength of the waves, then Doppler’s effect is taken into consideration.
As per Doppler’s effect, The frequency of the wave changes during the relative motion between the source of the wave and the observer.

Step II:
Since wavelength varies inversely with the frequency, so if frequency changes then wavelength will also change. As an object moves away from the observer, the light waves emitted by the object are stretched, then light moves towards the red side of the spectrum. It is called red shift. On the red side of the spectrum, waves have least frequency so their wavelength increases.

Step III:
But when an object is coming close to the observer, there will be more light waves emitted. The light moves towards the blue side of the spectrum. It’s frequency increases and wavelength decreases.

Step IV:
This is the reason that when an object is coming towards us, we are able to see it more clearly. But when it moves away from us, then it is not visible.

Note: Since white light of spectrum has seven colors VIBGYOR. The astronomers use this phenomenon to determine the motion of the cosmic objects. The cosmic objects change their color with time and astronomers can determine whether the object is approaching towards them or moving away from them.