THE DOPPLER EFFECT
1 mark · EasyState what is meant by red-shift in the context of galaxies.
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Red-shift is the increase in wavelength of light from a galaxy as it moves away from the observer.
Also accept: The light from a galaxy is stretched to longer wavelengths as it moves away.; Red-shift refers to the movement of spectral lines towards the red end of the spectrum when a galaxy is moving away.
Common mistakes: Confusing with blue-shift.; Mistaking red-shift for a change in brightness.
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Marking points
B1 · 1 mark · Clear statement that red-shift means an increase in observed wavelength from a galaxy moving away from the observer.
Worked solution
Red-shift is when light from a galaxy has its wavelength increased as the galaxy moves away from us.