• The Doppler effect affects all types of waves, including?light
• Light emitted from stars and galaxies will be at a certain wavelength in the visible part of the electromagnetic spectrum
• If an object moves?away?from an observer the?wavelength?of light?increases
  • This is known as?redshift?as the light moves towards the red end of the spectrum

   

• If an object moves?towards?an observer the?wavelength?of light?decreases
  • This is known as?blueshift?as the light moves towards the blue end of the spectrum

   

Light from a star that is moving towards an observer will be blue shifted and light from a star moving away from an observer will be red shifted

• An?increase?in wavelength is a?decrease?in frequency and vice versa

The observer in front observes a blue shift, the observer behind observes a redshift

• Galactic redshift provides evidence for the Big Bang Theory and the expansion of the universe
• The diagram below shows the?light?coming to us from a?close object, such as the Sun, and the light coming to the Earth from a?distant galaxy

Comparing the light spectrum produced from the Sun and a distant galaxy

Red-shift provides evidence that the Universe is expanding because:

• Red-shift is observed when the spectral lines from the distant galaxy move closer to the?red?end of the spectrum
  • This is because light waves are?stretched?by the expansion of the universe so the wavelength increases (or frequency decreases)
  • This indicates that the galaxies are moving?away?from us

   

• Light spectrums produced from?distant?galaxies are red-shifted?more?than?nearby?galaxies
  • This shows that the?greater?the?distance?to the galaxy, the?greater?the?redshift
  • This means that the?further away?a galaxy is, the?faster?it is moving away from the Earth

   

• These observations imply that the universe is?expanding?and therefore?support?the Big Bang Theory

Graph showing the greater the distance to a galaxy, the greater the redshift

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