Manejje
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What is the red shift?
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Vetofferholder1
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Astronomers can observe light from distant galaxies. When they do this, they see it is different to the light from the Sun. The dark lines in the spectra from distant galaxies show an increase in wavelength. The lines are moved or shifted towards the red end of the spectrum. This effect is called red-shift.
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Rhys_M
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(Original post by Manejje)
What is the red shift?
The Doppler effect is the apparent change in frequency and wavelength of a wave due to relative motion between the wave's source and its observer (you don't need to know this for GCSE).
This is why the pitch of an ambulence siren seems to change as it travels past you: the wave gets compressed as it moves towards you, and a higher frequency means higher pitch.

The same thing happens with light from distant galaxies.
We can observe light from distant galaxies using spectra, and find that the spectral lines are different from those of light from the sun - the light from the galaxies are shifted towards the red end of the visible light spectrum.
This stretching of the light from our perspective (increased wavelength) indicates that the galaxies are moving away, and so acts as evidence for The Big Bang Theory.
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