Christian Andreas Doppler

The Doppler effect as the universal key to movements in space

Christian Andreas Doppler (1803-1853), physicist and mathematician

Christian Andreas Doppler was born at the 29th of November 1803 in Salzburg as a son of a stone-mason. His mathematical ability was discovered by the teacher Simon Stampfer at the local gymnasium early. The teacher was moving to the Vienna technical highschool, and there he took with him also his best student.

Doppler finished his studies in Vienna in 1835 and became an assistant for higher mathematics, but he didn't get a fixed employment. Within this unsecure situation je was already prepared to emigrate to the U.S.A., but then he got the chance for an employment as the mathematics teacher at a secondary school in Prague, which was part of the kingdom Austria-Hungary at that time. Six years he remained as a teacher at that school, and it was within that time he got an illness from he never recovered until his death: tuberculosis. He was approved as a professor in physics at the Prague technical university in 1841. In this position he published a twenty page work in 1842 which made him become famous: "Über das farbige Licht der Doppelsterne und einiger anderer Gestirne des Himmels" (about the coloured light of double star systems and some other stars of the sky).

Within the first half of the 19th century the development and spreading of the railway network took place, and with the trains as the fastest mobile everyone could suddenly experience the phenomenon, that the pipe of a train sounded higher at its approach than after its pass-by. Doppler realized this phenomenon as an effect because of the nature of waves in that way that the sound waves of an approaching object were compressed through the speed difference between the moving and the non-moving system. Because of this compression the perceptor received more waves per time and this was causing the higher tone resp. the higher frequency. On the other hand, when a sounding object was moving away from the perceptor, the sound waves were streched through the speed difference, a lesser number of waves per time were reaching the perceptor who was perceiving this as a lower tone resp. a lower frequency. The relative speed in the direction of the axis of sight to the perceiver is also called radial velocity. Exactly this became measurable through the Doppler effect.

Sheliak-Animation
In his work Doppler tried to apply his discovery on the stars to explain the colors of the stars. Doppler wrote (cite according to K. H. Schwarz, translated): One might be strongly attracted to the opinion, that all stars of the sky might shine within a white or light yellowish light and that, if this is to be found different on other, a reason has to exist for this which might relate most probably with their high velocity of movement not only by random but by a necessary connection. [...]
Out of this it explains itself most easily:
1. Why the bigger and therefore most often not moving central star of two stars in a double star system is white with nearly no exception, while the other is most often colored!
2. Why in the latter case the one nearly always is shining in a light out of the upper part of the color spectrum (that is green, blue, violet), while the other one is shining in a light out of the lower part (that is red, orange, or yellow). Because for double stars with a similar size it can be assumed properly that the one (more violet one) is approaching, while the other (more reddish one) is withdrawing from us.

If Doppler would had been an astronomer, then he might had tried to justify his work with visual observations prior to the publishing. He might had found that the visible colors of double stars are not changing constantly and he might had found double star systems where two stars are moving around a common point between them, but where one star would had a color towards reddish or blueish and the other one somehat of white or yellow. And he might had found several other stars and star systems which had contradicted his assumptions. Its not predictable what this had meant to his publication. But Doppler was physicist and mathematician. He noted his theory without any consideration of reality in his work as a formular, which looks simplified like:


   v = (Δλ · c) / λ    

Within this formula v is placeholder for the relative velocity of an objects in the direction of the perceptor, Delta lambda (resp. Δλ) is the difference of measured and original wave length from the emitter, c is the constant maximum emitting speed of the waves (the "speed of sound" or "speed of light"), and lambda (resp. λ) is the original wave length from the emitter. The formula says: One can measure the radial velocity of an emitter by relating the frequency of the incoming waves to the emitted waves. If this speed has a positive value the emitter is leaving, if this speed has a negative value the emitter is closing up.

Algol-Animation
The possibility to evaluate the speed of a moving object through the measurement of the frequency change was tested only a few years after Doppler's publishing in the Netherlands with trains. It was the first traffic speed limit control of the world - many decades before the invention of the mass producted car, the autobahn, speed limit, traffic regulated zones, etc. pp.

In the year 1849 Doppler returned to Vienna after two years intermediate residence in Chemnitz. He became teacher for physics at the technical highschool of Vienna as the successor of is former mentor. Through his initiative an institute for physics was installed at the university of Vienna, and he became the director in 1851. But his illness cought in Prague was proceeding, and so he moved to Venice, because the rumour had it that the physicians there were able to cure tuberculosis. But at March 17, 1853 Doppler died because of his illness in Venice, not reaching an age of 50.

*

Algol-Spectrum-Animation
As known today, the visible colors of the stars are mainly influenced by the surface temperature of them: the more blueish a star, the hotter its surface. The change of color through the movement of stars can be noticed optically only in extreme cases. Nevertheless, the light of radial moving stars is altered...

In 1859 the chemists Robert Wilhelm Bunsen (1811-1899) and Gustav Robert Kirchhoff (1824-1887) developed the spectrum analysis through the evaporation of materials in flames, the spreading of the resulting light through prisms and the identification of distinctive visible lines within the spectrum as specificly ionized elements. The spectrum analysis together with the Doppler effect made it possible to show the radial movement of stars, because typical spectral lines of a star normally don't appear within the spectrum where they should, but normally they are shifted into the red or into the blue. This shift - interpreted as the Doppler effect - shows how a "fix" star is moving towards our Sun resp. towards Earth.

The shown animation of a spectrum is related to the animation of Algol (overemphasized, idealized, and for simplification drawn as an absorbtion spectrum) and it shows how a selection of spectral lines of the two stars would change over time: while the line set of the somewhat fixed star would also nearly show no changes, the set of spectral lines of the circelling star would move towards the blueish band when the star is moving along the line of view towards the viewer and would move into the reddish band when the star is moving along the line of view away from the viewer. In reality not only the one line set, but also the other would show a reverse movement, but with a many times lesser amplitude. In fact because of further tiny and long time periodic changes of the spectral lines of Algol it was possible to conclude that also a third sun is moving around the central stars within a distance of two astronomical units, while the two main suns only have a distance of about 10 million kilometer (or 0.07 astronomical units). One of the first spectroscopical analysis of these occultating variable stars (see also John Goodricke) of Algol were done by Carl Hermann Vogel (1841-1907) in 1888/9 at the Potsdam observatory.

Saturn ring spectrums
With the spectral analysis of stars within galaxies it was possible to prove that they are gigantic circeling disks. - The long time spectral analysis of single stars and the detection of weak, long periodic changes is also used as a possible method to find planets of lesser-than-Jupiter-mass around distant suns, maybe even to find Earth-like planets within the tropical belt of a star. - With the systematic measurement of the overall spectrums of galaxies and the discovery that the upmost number of galaxies have a red shift of their spectrum, Edwin Powell Hubble (1889-1953) evolved his theory of the expanding universe. In fact it was found that galaxies have generally a higher redshift the farther they are away. And with this analysis it was also possible to evaluate the movement of our milkyway towards the constellation of Virgo and the Virgo cluster.

But also non self emitting objects can be analized according to their radial velocity through the Doppler effect, if they at least reflect some radiation. Through the reflection parts of the incoming radiation are absorbed, and also these parts can be analized through their spectral lines, and also their shift. Therefore the Doppler effect was also measureable at the rings of Saturn, and with this it was possible to proof the deductions of Christian Huygens (1629-1695) out of the Kepler laws, that the rings of Saturn cannot be a single solid object. Analog, the Doppler effect can be used to measure the rotation of planetoids and any other movements of objects in space.

In the Haus der Natur, Salzburg is (or at least was in 1999) a special exhibition about Christian Andreas Doppler and his work (, which is or at least wasn't mentioned online in November 2002). This exhibition shows also further applications of the Doppler effect on Earth.

Sources:
Prof. Dr. K. H. Schwarz, "Physik- und Radiopioniere", Verlag Wetzikon 1971
Prof. Mag. DDr. h.c. Eberhardt Stüber et al., "Haus der Natur", Haus der Natur 1999
Joachim Herrmann (ed.), "Das Große Lexikon der Astronomie", Orbis Verlag 1996


Page history:
created 2003-08-06 from sky.03.11.html
modified 2003-08-06 to Doppler-e.html

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