Christian Johann Doppler: the man behind the effect.

The Doppler effect is the apparent difference between the frequency at which waves (sound or light) leave a source and that at which they reach an observer, caused by relative motion of the observer and the wave source [1]. For example, if a source of sound of a constant pitch is moving towards an observer, the sound seems higher in pitch, whereas if the source is moving away, it seems lower. As one approaches a blowing horn, the perceived pitch is higher until the horn is reached and then becomes lower as the horn is passed. Similarly, the light from a star, observed from the Earth, shifts towards the red end of the spectrum (lower frequency or longer wavelength) if the Earth and star are receding from each other and towards the violet (higher frequency or shorter wavelength) if they are approaching each other. By measuring this shift, the relative motion of the Earth and star can be calculated. The Doppler effect is an integral part of modern theories on the beginning of the universe (the Big Bang and the red shift). It is used today for weather forecasting, in radar and modern navigation, in studying the motion of stars and is widely used in the diagnosis of cardiovascular diseases. The effect takes its name from the Austrian physicist Christian Johann Doppler. Who was this man who gave us the tools to explore these divergent and different subjects? Christian Johann Doppler was born 29 November 1803 in Salzburg, Austria [2–5] (Figure 1). He came from a family of master stonemasons who had had a successful business in Salzburg since 1674 [6]. Naturally, the family tradition would have had him grow up to take over the stonemasonry business. However, Doppler’s health was never very good and he was quite frail, so he could not follow in the family tradition. Because of Doppler’s poor health, his father considered him suitable for the book-keeping function of the family business. Doppler attended primary school in Salzburg and secondary school in Linz. However, it soon became apparent that Doppler had outstanding talents in mathematics. His parents consulted the professor of mathematics at the Salzburg Lyceum who recommended that Doppler should study mathematics at the Vienna Polytechnic Institute (today’s Vienna University of Technology). The Polytechnic Institute had only been founded in 1815, so it was still a new establishment when Doppler began his studies there in 1822 [2]. He excelled in his mathematical and other studies and graduated in 1825. After this, at the age of 21, he returned to his native Salzburg and finished his education (philosophy lectures at the Salzburg Lyceum) while supporting himself by giving classes in mathematics and physics. Then, for the next 4 years, he went to the University of Vienna where he studied higher mathematics, mechanics and astronomy. At the end of his studies at the University of Vienna in 1829, Doppler was appointed as assistant to Professor Burg, the professor of higher mathematics and mechanics at the University. During his 4 years as Burg’s assistant,