THE DOPPLER EFFECT
2 marks · NormalA student incorrectly states that the blue-shift of galaxy light proves the universe is expanding. Explain why this statement is incorrect.
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Blue-shift means an object is moving towards us, not away. The universe’s expansion is evidenced by red-shift, where most galaxies are moving away from us.
Also accept: Blue-shift shows approach, not recession/expansion.
Common mistakes: Simply saying blue-shift is not evidence, without explaining direction
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Marking points
B1 · 1 mark · States blue-shift means approaching (not receding/expanding).
B1 · 1 mark · Links red-shift to expansion (most galaxies), not blue-shift.
Worked solution
Blue-shift means a galaxy is moving towards us, not away. Expansion is shown by red-shift, when galaxies are moving away from us.