How was the doppler effect discovered?
The Austrian mathematician and physicist, Christian Doppler, developed the theory in 1842 to explain the colours of binary stars.
He argued that the observed frequency of an electromagnetic save or sound wave depends on the relative speed of the source and the observer.
The change in frequency is called the Doppler effect or Doppler shift .
A sound that is approaching you will seem higher than it really is. If the sound is going away from you, it will seem lower than its actual pitch.
To test Doppler's theory, the Dutch meteorologist Christoph Ballot in 1843 hired 15 trumpeters with precisely-tuned instruments to play on a train as it passed by stationary musicians.
They heard a drop in pitch as the train passed by, just as Doppler predicted.