Doppler, Christian Johann (1803–1853)

Austrian physicist who in 1842 described the Doppler effect and derived the observed frequency mathematically in Doppler's principle.

Doppler was born in Salzburg and attended the Polytechnic Institute in Vienna. In 1835 he went to Prague to teach mathematics; in 1850 he became director of the new Physical Institute at the Royal Imperial University of Vienna.

The first experimental test of Doppler's principle was made 1845 in Utrecht in the Netherlands. A locomotive was used to carry a group of trumpeters in an open carriage to and fro past some musicians able to sense the pitch of the notes being played. The variation of pitch produced by the motion of the trumpeters verified Doppler's equations.

Doppler correctly suggested that his principle would apply to any wave motion. He believed that all stars emit white light and that differences in colour are observed on Earth because the motion of stars affects the observed frequency of the light and hence its colour. In fact, stars vary in their basic colour, but it is possible to use the red shift to determine the distances of galaxies.