The Austrian physicist and mathematician, Christian Doppler was born in Salzburg in 1803, the son of a stonecutter. He studied Mathematics and Physics at the Polytechnisches Institut in Vienna, and Philosophy at the University of Salzburg. In 1835, after a period as an assistant professor in Vienna, he obtained a post as a professor at the University of Prague, then the second most important city in Austria-Hungary.
In 1842, he presented a paper that made him famous worldwide: On the Coloured Light of Double Stars and Some Other Heavenly Bodies. In this paper he hypothesised that certain properties of light emitted from stars depend upon the relative motion of the observer and the wave source. He suggested that the coloured appearance of some stars was caused by their motion relative to the Earth, the blue ones moving toward Earth and the red ones moving away.
He drew an analogy of a ship moving to meet, or retreat from, incoming waves. The ship moving out to sea would meet the waves quicker than a ship moving toward the shoreline.
This phenomenon was readily applicable to sound waves also: the apparent pitch of a sound changes if the source of the sound is moving relative to an observer.
To test his hypothesis, Doppler used two sets of trumpeters: one set standing still at a train station and one set moving on an open train car. Both sets of musicians had perfect pitch and held the same note. As the train passed the station, it could be clearly heard that the frequency of the moving trumpets was different, even though all the musicians were playing the same note. This proved Doppler's hypothesis. Later, a scientist named Fizeau generalized Doppler's work to apply his theory to astronomy.
In 1848 Doppler returned to Vienna as a member of the Academy of Science and as a professor at the Polytechnisches Institut. Then, in 1850, the Emperor Franz Josef created a new Institute of Physics and Doppler was appointed its first director.
While on holiday in Venice in 1853 he died of a lung illness, due to long exposure to his father's dusty workshop as a child.