On November 29, 1803, mathematician Christian Andreas Doppler was born in Austria. Although primarily a teacher of mathematics, he also studied astronomy and eventually became the Director of the Institute of Physics at the University of Vienna. The years in between were filled with episodes of frail health, unhappy job seeking and teaching woes. Doppler did write papers on several subjects but most fell short of the acceptance he sought.
His most inspired work seemed to be in conceptualizing. Doppler had many interests from his various studies in maths and physics and was a keen observer. In small groups and one-on-one meetings, he stimulated colleagues with questions, ideas, and his insight. To one science society, Doppler presented a paper On the Coloured Light of Double Stars and Certain Other Stars of the Heavens and triggered unending interest and discussion.
He postulated that the speed or velocity of a source could create changes in how we perceived sound and light. Doppler demonstrated that the pitch of sound changes when the source of the sound moves toward us or moves away from us. We hear this phenomenon every time an ambulance siren or train horn comes toward us and passes us – the higher pitch upon approach becomes noticeably lower as the vehicle leaves.
Since both sound and light travel as waves, Doppler reasoned that this effect applied to light waves if the source of the light were moving. Although he assumed that the natural colour of stars was white, he predicted that a star moving toward or away from Earth would be perceived according to the shortest or longest light waves visible to the Earth observer. Starlight moving toward us would be perceived as violet, the light of shortest wavelength, while the light from a star moving away from us would appear red, the light wave of longest length. Decades later, as astronomy tools evolved, stars revealed their many colours and temperatures, and red wavelengths were indeed visible.
In grouping wave phenomena of both sound and light, Doppler’s intuition about waves took the theories of his time one step forward. Introducing variation in velocity of waves has sparked thought, research, and application that continue to this day. The Doppler Effect he described provided a basic premise for radar and sonar and the eventual work with the redshift phenomena of distant stars that support the idea that our universe is expanding.
B Bondar / Real World Content Advantage