REDSHIFT

Doppler Effect
When there is a relative motion between the source of waves and the observer, the frequency of wave produced by a source and the frequency received by the observer is different. This effect is known as doppler effect.

Doppler Effect proved that -

1.When the source approaches a stationary observer the wavelengths of waves emitted from source become smaller. So, apparent frequency increases.

As a result, pitch of sound increases.

2.When the source moves away from the stationary observer, the wavelengths of waves emitted from source become larger. So, apparent frequency decreases.

As a result, pitch of sound decreases.

3.When the observer approaches the source , pitch of sound increases. f increases.

4.When the observer recedes from the source , pitch of sound decreases.

REDSHIFT
Light emitted from an object moving away from you will have its wavelength lengthened.

BLUESHIFT
Light emitted from an object moving towards you will have its wavelength shortened.