red shift (physics)

Whenever there is a relative motion between the observer and the source, there is a change in wavelength (frequency) of the wave observed due to Doppler effect.

When the two objects are moving apart from each other, the wavelength of the observed wave will increase (frequency decreases) (And for the case of light, red shift occurs.)


When the two objects are moving towards each other, the wavelengthof the observed wave will decrease (frequency increases) (And for thecase of light, blue shift occurs.)


The speed of the wave will not be affected by the motion of the wave source. It is because the speed of the wave only depends on the characteristic of the medium (For light, it does not necessary need a medium to propagate)


Red shift means the observed wavelength of the light increases relative to the original wavelength (wavelength increases, so that it is closer to the red colour in the spectrum) since the observer and the source are moving apart from each other.

Blue shift means the observed wavelength of the light decreases relative to the original wavelength (wavelength decreases, so that is is closer to the violet colour in the spectrum) since the observer and the source are moving towards each other.


When you hear a pitch changing from high to low, the source and the observer are moving apart from each other and now they are at the moment of passing each other.