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Person

Christian Doppler

A portrait of Christian Doppler, wearing formal attire with a bow tie, set against a dark background.

Austrian mathematician and physicist (1803–1853) who proposed in an 1842 Prague paper that the observed frequency of a wave depends on the relative motion of source and observer. He applied the idea to starlight, expecting it to shift the colours of binary stars; the effect is real but far too small at stellar velocities to register as a change of visible colour. The principle bears his name and underlies radar, sonar, and modern cosmology.

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