Red Shift

The Doppler Effect

This effect can be heard when a formula 1 car drives past you. As the car approaches you the sound it produces is higher pitched than when it drives away from you, where the sound becomes lower in pitch.

When the sound source moves towards you to wavelength decreases and the frequency of the sound increase (higher pitch).

doppler towards

When the sound source moves away from you the wavelength increases and the frequency of the sound decrease (lower pitch).

doppler away

Red Shift

When the light from a galaxy which is moving away from you is observed the  wavelength of the observed light appears longer, it moves towards the red end of the spectrum. This is called RED SHIFT.


White light can be split up into its component colours using a prism or diffraction grating. The colours from short wavelength to long are;


  • violet
  • indigo
  • blue
  • green
  • yellow
  • orange
  • red


spectrum line 1

The observed wavelength of the light is longer when objects are moving away from us. The light is shifted towards the red end of the spectrum, RED SHIFT.

spectrum line 2

The Big Bang

Red shift supports the big bang theory.

The big bang theory is that the universe began from a very small initial point. The universe then expanded from that point to give us the universe we see today.

The light from distant galaxies is red shifted (this tells us the galaxies are moving away from us) and the further away the galaxy the greater the red shift (this tells us that the more distant the galaxy the faster it is moving).

Cosmic Background Microwave Radiation (CMBR)

A second piece of evidence that supports the big bang theory is cosmic background microwave radiation.  Electromagnetic radiation which was present shortly after the big bang is now observed as background microwave radiation.

COBE background microwave image