Über das farbige Licht der Doppelsterne und einiger anderer Gestirne des Himmels
Encyclopedia
Christian Doppler
Christian Andreas Doppler was an Austrian mathematician and physicist.-Life and work:Christian Doppler was raised in Salzburg, Austria, the son of a stonemason. Doppler could not work in his father's business because of his generally weak physical condition...
(1842) in which he postulated his principle that the observed frequency changes if either the source or the observer is moving, which later has been coined the Doppler effect
Doppler effect
The Doppler effect , named after Austrian physicist Christian Doppler who proposed it in 1842 in Prague, is the change in frequency of a wave for an observer moving relative to the source of the wave. It is commonly heard when a vehicle sounding a siren or horn approaches, passes, and recedes from...
. The original German text can be found in wikisource. The following annotated summary serves as a companion to that original.
Summary
The title "" (On the coloured light of the binary stars and some other stars of the heavens - Attempt at a general theory including Bradley's theorem as an integral part) specifies the purpose: describe the hypothesis of the Doppler effect, use it to explain the colours of binary stars, and establish a relation with Bradley's stellar aberration.§ 1 Introduction in which Doppler reminds the readers that light is a wave, and that there is debate as to whether it is a transverse wave
Transverse wave
A transverse wave is a moving wave that consists of oscillations occurring perpendicular to the direction of energy transfer...
, with aether particles oscillating perpendicular to the propagation direction. Proponents claim this is necessary to explain polarised light, whereas opponents object to implications for the aether. Doppler doesn't choose sides, although the issue returns in § 6.
§ 2 Doppler observes that colour is a manifestation of the frequency of the light wave, in the eye of the beholder. He describes his principle that a frequency shift occurs when the source or the observer moves. A ship meets waves at a faster rate when sailing against the waves than when sailing along with them. The same goes for sound and light.
§ 3 Doppler derives his equations for the frequency shift, in two cases:
| Equation Doppler | Modern equation | ||
| 1. | Observer approaching stationary source with speed vo | n/x = (a + αo)/a | f ' / f = (c+vo) / c |
| 2. | Source approaching stationary observer with speed vs | n/x = a/(a - αs) | f ' / f = c / (c-vs) |
§ 4 Doppler provides imaginary examples of large and small frequency shifts for sound:
| vo = -c | f ' = 0 | frequency shift down to inaudibly low tones |
| vs = -c | f ' / f = 0.5 | frequency shift down over 1 octave, still audible. |
| vo = +c | f ' / f = ∞ | frequency shift up to inaudibly high tones |
| vo = 40 m/s | C to D | note C shifting to D. |
| vo = 5.4 m/s | quarter note | threshold for best observers with absolute hearing |
§ 5 Doppler provides imaginary examples of large and small frequency shifts for light from stars. Velocities are expressed in Meilen/s, and the light speed has a rounded value of 42000 Meilen/s. Doppler assumes that 458 THz (extreme red) and 727 THz (extreme violet) are the borders of the visible spectrum, that the spectrum emitted by stars lies exactly between these borders (except for the infrared stars of § 8), and that the colour of the light emitted by stars is white.
| Meilen/s | km/s | f ' / f | |
| vs = -19000 | 141000 | 458 / 727 | shift from extreme violet to extreme red, and from other colours to invisible range beyond extreme red |
| vs = -5007 | 37200 | 458 / ? | shift from yellow to extreme red |
| vs = -1700 | 12600 | 458 / ? | shift from red to extreme red |
| vs = -33 | 244 | 458 / 458.37 | threshold for visual perception of colour changes shift from a shade of red to next shade of red approaching white star gets a green shade receding white star gets an orange shade |
§ 6 Doppler summarises:
- The natural colour of stars is white or a weak yellow.
- A white star receding with progressive speed would successively turn to green, blue, violet, and invisible (ultraviolet).
- A white star approaching with progressive speed would turn to yellow, orange, red, and invisible (infrared).
Doppler wishes that his frequency shift theory will soon be tested by another method to determine the radial velocity of stars. He thinks, without reason, that a confirmation of his theory would imply that light is not a transverse but a longitudinal wave.
Christian Doppler
Christian Andreas Doppler was an Austrian mathematician and physicist.-Life and work:Christian Doppler was raised in Salzburg, Austria, the son of a stonemason. Doppler could not work in his father's business because of his generally weak physical condition...
(1842)Some sources mention 1843 as year of publication because in that year the article was published in the Proceedings of the Bohemian Society of Sciences
Bohemian Society of Sciences
Bohemian Society of Sciences is the first official scientific organization within Bohemia.-History:The Bohemian Society of Sciences was created from the Private Society for Mathematics, Patriotic History and Natural History, the first scientific society within the frontiers of the later...
. Doppler himself referred to the publication as "Prag 1842 bei Borrosch und André", because in 1842 he had a preliminary edition printed that he distributed independently. in which he postulated his principle that the observed frequency changes if either the source or the observer is moving, which later has been coined the Doppler effect
Doppler effect
The Doppler effect , named after Austrian physicist Christian Doppler who proposed it in 1842 in Prague, is the change in frequency of a wave for an observer moving relative to the source of the wave. It is commonly heard when a vehicle sounding a siren or horn approaches, passes, and recedes from...
. The original German text can be found in wikisource. The following annotated summary serves as a companion to that original.
Summary
The title "" (On the coloured light of the binary stars and some other stars of the heavens - Attempt at a general theory including Bradley's theorem as an integral part) specifies the purpose: describe the hypothesis of the Doppler effect, use it to explain the colours of binary stars, and establish a relation with Bradley's stellar aberration.§ 1 Introduction in which Doppler reminds the readers that light is a wave, and that there is debate as to whether it is a transverse wave
Transverse wave
A transverse wave is a moving wave that consists of oscillations occurring perpendicular to the direction of energy transfer...
, with aether particles oscillating perpendicular to the propagation direction. Proponents claim this is necessary to explain polarised light, whereas opponents object to implications for the aether. Doppler doesn't choose sides, although the issue returns in § 6.
§ 2 Doppler observes that colour is a manifestation of the frequency of the light wave, in the eye of the beholder. He describes his principle that a frequency shift occurs when the source or the observer moves. A ship meets waves at a faster rate when sailing against the waves than when sailing along with them. The same goes for sound and light.
§ 3 Doppler derives his equations for the frequency shift, in two cases:
| Equation DopplerDoppler uses other symbols for the variables than we usually do today: f = 1/n, f ' = 1/x, vo = αo, vs = αs. (Note n=n" and x=x", as in number of seconds = time). | Modern equation | ||
| 1. | Observer approaching stationary source with speed vo | n/x = (a + αo)/a | f ' / f = (c+vo) / c |
| 2. | Source approaching stationary observer with speed vs | n/x = a/(a - αs) | f ' / f = c / (c-vs) |
§ 4 Doppler provides imaginary examples of large and small frequency shifts for sound:
| vo = -c | f ' = 0 | frequency shift down to inaudibly low tones |
| vs = -c | f ' / f = 0.5 | frequency shift down over 1 octave, still audible. |
| vo = +c | f ' / f = ∞ | frequency shift up to inaudibly high tonesinaudible, except for the shock wave ignored by Doppler. |
| vo = 40 m/s1 par.Fuss Paris inch The Paris inch, or pouce, is an old unit of measure, that among other uses, was common for giving the measurement of lenses. The Paris inch could be subdivided into 12 ligne , and 12 Paris inches made a Paris foot. The Paris inch and Paris foot could be abbreviated with " and ' like some other... = 0.325 m (pied de roi); speed of sound 1024 par.Fuss/s = 333 m/s |
C to D | note C shifting to D. |
| vo = 5.4 m/s | quarter note | threshold for best observers with absolute hearingIn 1845 Buys Ballot used this idea of musicians with absolute hearing for the first experimental verification of the Doppler effect. |
§ 5 Doppler provides imaginary examples of large and small frequency shifts for light from stars. Velocities are expressed in Meilen/s, and the light speed has a rounded value of 42000 Meilen/s.Meile = geografische Meile = 7420 m. Doppler provides the rounded value of 42000 Meilen/s instead of the best accurate value of his time. The rounded value was well known and stable throughout the years, whereas the accurate value varied due to frequent new measurements. Since 1835 the accurate value was 41549 geogr. Meilen/s (308000 km/s), see Pierer's Universallexikon and Wüllner's Experimentalphysik Doppler assumes that 458 THz (extreme red) and 727 THz (extreme violet) are the borders of the visible spectrum, that the spectrum emitted by stars lies exactly between these borders (except for the infrared stars of § 8), and that the colour of the light emitted by stars is white. These assumptions are wrong. Doppler ignores the emitted infrared and ultraviolet, although their presence in sun light was known since studies by Herschel (1800) and Ritter (1801). As a result Doppler overstimates the visual colour changes. He knew that stars are able to emit infrared, as he proposes so in § 8. With regard to the colours of stars, the assumption that stars emit white light is his major mistake. Nowadays we know that colour mainly depends on the star temperature.
§ 6 Doppler summarises:
- The natural colour of stars is white or a weak yellow.
- A white star receding with progressive speed would successively turn to green, blue, violet, and invisible (ultraviolet).
- A white star approaching with progressive speed would turn to yellow, orange, red, and invisible (infrared).
Doppler wishes that his frequency shift theory will soon be tested by another method to determine the radial velocity of stars. He thinks, without reason, that a confirmation of his theory would imply that light is not a transverse but a longitudinal wave.
Christian Doppler
Christian Andreas Doppler was an Austrian mathematician and physicist.-Life and work:Christian Doppler was raised in Salzburg, Austria, the son of a stonemason. Doppler could not work in his father's business because of his generally weak physical condition...
(1842)Some sources mention 1843 as year of publication because in that year the article was published in the Proceedings of the Bohemian Society of Sciences
Bohemian Society of Sciences
Bohemian Society of Sciences is the first official scientific organization within Bohemia.-History:The Bohemian Society of Sciences was created from the Private Society for Mathematics, Patriotic History and Natural History, the first scientific society within the frontiers of the later...
. Doppler himself referred to the publication as "Prag 1842 bei Borrosch und André", because in 1842 he had a preliminary edition printed that he distributed independently. in which he postulated his principle that the observed frequency changes if either the source or the observer is moving, which later has been coined the Doppler effect
Doppler effect
The Doppler effect , named after Austrian physicist Christian Doppler who proposed it in 1842 in Prague, is the change in frequency of a wave for an observer moving relative to the source of the wave. It is commonly heard when a vehicle sounding a siren or horn approaches, passes, and recedes from...
. The original German text can be found in wikisource. The following annotated summary serves as a companion to that original.
Summary
The title "" (On the coloured light of the binary stars and some other stars of the heavens - Attempt at a general theory including Bradley's theorem as an integral part) specifies the purpose: describe the hypothesis of the Doppler effect, use it to explain the colours of binary stars, and establish a relation with Bradley's stellar aberration.§ 1 Introduction in which Doppler reminds the readers that light is a wave, and that there is debate as to whether it is a transverse wave
Transverse wave
A transverse wave is a moving wave that consists of oscillations occurring perpendicular to the direction of energy transfer...
, with aether particles oscillating perpendicular to the propagation direction. Proponents claim this is necessary to explain polarised light, whereas opponents object to implications for the aether. Doppler doesn't choose sides, although the issue returns in § 6.
§ 2 Doppler observes that colour is a manifestation of the frequency of the light wave, in the eye of the beholder. He describes his principle that a frequency shift occurs when the source or the observer moves. A ship meets waves at a faster rate when sailing against the waves than when sailing along with them. The same goes for sound and light.
§ 3 Doppler derives his equations for the frequency shift, in two cases:
| Equation DopplerDoppler uses other symbols for the variables than we usually do today: f = 1/n, f ' = 1/x, vo = αo, vs = αs. (Note n=n" and x=x", as in number of seconds = time). | Modern equation | ||
| 1. | Observer approaching stationary source with speed vo | n/x = (a + αo)/a | f ' / f = (c+vo) / c |
| 2. | Source approaching stationary observer with speed vs | n/x = a/(a - αs) | f ' / f = c / (c-vs) |
§ 4 Doppler provides imaginary examples of large and small frequency shifts for sound:
| vo = -c | f ' = 0 | frequency shift down to inaudibly low tones |
| vs = -c | f ' / f = 0.5 | frequency shift down over 1 octave, still audible. |
| vo = +c | f ' / f = ∞ | frequency shift up to inaudibly high tonesinaudible, except for the shock wave ignored by Doppler. |
| vo = 40 m/s1 par.Fuss Paris inch The Paris inch, or pouce, is an old unit of measure, that among other uses, was common for giving the measurement of lenses. The Paris inch could be subdivided into 12 ligne , and 12 Paris inches made a Paris foot. The Paris inch and Paris foot could be abbreviated with " and ' like some other... = 0.325 m (pied de roi); speed of sound 1024 par.Fuss/s = 333 m/s |
C to D | note C shifting to D. |
| vo = 5.4 m/s | quarter note | threshold for best observers with absolute hearingIn 1845 Buys Ballot used this idea of musicians with absolute hearing for the first experimental verification of the Doppler effect. |
§ 5 Doppler provides imaginary examples of large and small frequency shifts for light from stars. Velocities are expressed in Meilen/s, and the light speed has a rounded value of 42000 Meilen/s.Meile = geografische Meile = 7420 m. Doppler provides the rounded value of 42000 Meilen/s instead of the best accurate value of his time. The rounded value was well known and stable throughout the years, whereas the accurate value varied due to frequent new measurements. Since 1835 the accurate value was 41549 geogr. Meilen/s (308000 km/s), see Pierer's Universallexikon and Wüllner's Experimentalphysik Doppler assumes that 458 THz (extreme red) and 727 THz (extreme violet) are the borders of the visible spectrum, that the spectrum emitted by stars lies exactly between these borders (except for the infrared stars of § 8), and that the colour of the light emitted by stars is white. These assumptions are wrong. Doppler ignores the emitted infrared and ultraviolet, although their presence in sun light was known since studies by Herschel (1800) and Ritter (1801). As a result Doppler overstimates the visual colour changes. He knew that stars are able to emit infrared, as he proposes so in § 8. With regard to the colours of stars, the assumption that stars emit white light is his major mistake. Nowadays we know that colour mainly depends on the star temperature.
§ 6 Doppler summarises:
- The natural colour of stars is white or a weak yellow.
- A white star receding with progressive speed would successively turn to green, blue, violet, and invisible (ultraviolet).
- A white star approaching with progressive speed would turn to yellow, orange, red, and invisible (infrared).
Doppler wishes that his frequency shift theory will soon be tested by another method to determine the radial velocity of stars. He thinks, without reason, that a confirmation of his theory would imply that light is not a transverse but a longitudinal wave.Bolzano, in his review in 1843, points out that Doppler's thought that his theory would not apply for transverse waves is a mistake.