What is Doppler shift: Definition and 148 Discussions

The Doppler effect or Doppler shift (or simply Doppler, when in context) is the change in frequency of a wave in relation to an observer who is moving relative to the wave source. It is named after the Austrian physicist Christian Doppler, who described the phenomenon in 1842.
A common example of Doppler shift is the change of pitch heard when a vehicle sounding a horn approaches and recedes from an observer. Compared to the emitted frequency, the received frequency is higher during the approach, identical at the instant of passing by, and lower during the recession.The reason for the Doppler effect is that when the source of the waves is moving towards the observer, each successive wave crest is emitted from a position closer to the observer than the crest of the previous wave. Therefore, each wave takes slightly less time to reach the observer than the previous wave. Hence, the time between the arrivals of successive wave crests at the observer is reduced, causing an increase in the frequency. While they are traveling, the distance between successive wave fronts is reduced, so the waves "bunch together". Conversely, if the source of waves is moving away from the observer, each wave is emitted from a position farther from the observer than the previous wave, so the arrival time between successive waves is increased, reducing the frequency. The distance between successive wave fronts is then increased, so the waves "spread out".
For waves that propagate in a medium, such as sound waves, the velocity of the observer and of the source are relative to the medium in which the waves are transmitted. The total Doppler effect may therefore result from motion of the source, motion of the observer, or motion of the medium. Each of these effects is analyzed separately. For waves which do not require a medium, such as electromagnetic waves or gravitational waves, only the relative difference in velocity between the observer and the source needs to be considered, giving rise to the relativistic Doppler effect.

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  1. P

    What Causes the Discrepancy in Doppler Shift for Satellites in Orbit?

    At page http://www.qsl.net/vk3jed/doppler.html" is discussed Doppler shift at various ham radio frequencies. I calculated for this Doppler shift relative velocity of their satellite as 6720 m/s. Their satellite in height of 800 km above ground and at circular orbit should have velocity of 7453...
  2. TrickyDicky

    Gravitational redshift from doppler shift

    Hi, I'm interested in the derivation of the gravitational redshift formula from the Doppler shift in an accelerated frame formula (or viceversa), that are linked by the Equivalence principle, it should be pretty straightforward but I get stuck. Anyone can show me this or point me to a link with...
  3. S

    Understanding Doppler Shift in Radio-Equipped Plumbing Vans

    Problem: Three radio-equipped plumbing vans are broadcasting on the same frequency,f0. Van 1 is moving north of van 2 with speed v, van 2 is fixed, and van 3 is moving west of van 2 with speed v. what change in frequency (f-f0) does van 3 hear from van 2? From van 1? Attempt at solution...
  4. F

    Calculating Circular Polar Orbit Parameters and Fractional Doppler Shift

    Hii guys.I have this problem.Can anybody help me on this.tq Homework Statement A satellite is in a circular polar orbit at a height of 870 km, the orbital period being approximately 102 min. The satellite orbit passes directly over a beacon at sea level. Assuming an average value of...
  5. D

    Doppler shift with microwaves i think

    Doppler shift with microwaves...i think... Homework Statement Microwaves, which travel at the speed of light, are reflected from a distant airplane approaching the microwave source. It is found that when the reflected waves are beat against the waves radiating from the source, the beat...
  6. M

    Relativistic Doppler Shift Theory Question?

    Homework Statement What sort of frequency shift does a rocket ship traveling along the x-axis as some speed close to c observe when it passes directly over a light source emitting photon on the y-axis (so when the angle between them is 90 degrees). At this angle, the rocket is neither...
  7. S

    Absolute velocity, CMB, and doppler shift

    I've heard it said that it is impossible to determine an objects absolute velocity, all one can do is find it relative to some other object... but, if the CMB is everywhere, why could you not just measure the doppler shift in all directions, and adjust your velocity so the CMB has no doppler...
  8. I

    Derivation of Doppler Shift from Frequency to Wavelenght

    Homework Statement Derive the doppler shift equation from the equation in terms of frequency to one in terms of wavelenght. Clues: frequency=c/lamda, use Taylor's expansion, velocity of source is much smaller than velocity of wave. c-velocity of wave v-velocity of source f-frequency...
  9. N

    SR and classical Doppler shift

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  10. A

    Maxwells equation and Doppler Shift.

    I am trying to grasp how Maxwell's equations and energy/photons are related in a doppler shift problem. The way I stated it seems to have attracted non-serious hecklers; so I am trying to restate the problem for people who know Maxwell's equations and are familiar with engineering. In...
  11. K

    Does the observed frequency approach infinity or does it become negative?

    I chose to write an essay on the "interesting" question I stumbled upon For part of it I am trying to calculate the Doppler shift in light with the relative motion of C. I suppose in the effort to not drone on for days I will first limit it to small, more simple questions and later,if we...
  12. C

    Doppler Shift for Traffic Light Colors

    Homework Statement How fast would a motorist have to be traveling for a yellow (l = 595 nm) traffic light to appear green (l = 550 nm) because of the Doppler shift? Homework Equations v=[(c)(f0/fs)2-c] / [(f0/fs)2+1] The Attempt at a Solution v= Speed of motorist c= Speed of light...
  13. B

    Are the formulas that account for aberraion and doppler shift compatible?

    Presenting the aberration of light effect we consider that two observers at rest in I and I' in the standard configuration equipped with laser guns start to emit light when they are instantly located at the same point in space. The problem is to find out a relationsship between the directions...
  14. B

    Validity of the Doppler shift formula?

    The formula which accounts for the Doppler shift is derived from the invarainace of the phase of a plane wave. [1] The plane wave is a mathematical construction associated with an infinite source os oscillation or with a very high source-receiver distance. The same formula is derived...
  15. C

    Any experimental evidence of Doppler shift in light?

    Were there any experiments that proved doppler shift of light on a fast moving object - that it has higher frequency if the object is moving towards you and lower if the object is moving away?
  16. A

    Doppler Shift and Velocity Relationship

    1. Whenever we talk about a single frequency characterizing an electromagnetic wave, we are tacitly assuming that the source and the detector are stationary relative to one another. However, if the distance between the two is changing in velocity, V, then the frequency of radiation, ν1 emitted...
  17. Loren Booda

    Does Hubble's law rely on the Doppler shift?

    If not Doppler, what type of transformation does Hubble's law utilize?
  18. P

    Would Gravity Waves Show Doppler Shift?

    Random question that I thought of while trying to fall asleep last night. :) We all know that galaxies moving very fast away from us exhibit visual redshift. If gravity waves / gravitons are real, they must then have a frequency of some kind. Does the frequency of a gravity wave affect...
  19. V

    Why is the Doppler shift expression sometimes reversed?

    Hello, I am well and truly stumped on Doppler shift. The complete expression is f'=f \gamma (1-\beta cos(\theta)) where: \beta=v/c v=source\ velocity \gamma=\frac{1}{\sqrt{1-\beta^{2}}} \theta is the angle between received photons (lab frame) and the direction of motion of...
  20. T

    Relativistic Doppler Shift and a Star breaking up

    Homework Statement A distant star at rest with respect to an observer on Earth emits light of frequency 6.690 x 10^14 Hz. The star breaks up into two remnants of equal mass, which are observed to emit light of frequency 7.135 x 10^14 Hz and 4.282 x 10^14 Hz Find the velocities of the...
  21. T

    Relativistic Doppler Shift Equation - Derivation

    Homework Statement The full expression for the relativitic Doppler Shift is v' = v \gamma [1- \beta cos \theta] where v' and v are the frequencies of the light source in its own rest frame and and in the laboraty respectivley. \theta is the (laboratory) anglebetween the direction of...
  22. Z

    How Does Doppler Shift Explain the Beats Heard from a Moving Car?

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  23. P

    . Radio Spectroscopy -> Finding the doppler shift in a graph

    I've been trying this for 3 hours and I'm getting nowhere. These are the graphs I made for Hydrogen Intensity vs Frequency for a radio telescope that transits the sun and galactic arms of the galaxy. http://img220.imageshack.us/img220/5904/helpgraphia6.jpg...
  24. S

    The Doppler Shift - is this right?

    Homework Statement The Doppler shift was first tested in 1845 by the French scientist B. Ballot. He had a trumpet player sound an A 440 Hz while riding on a flatcar pulled by a locomotive. At the same time, a stationary trumpeter played the same note. Ballot heard 3.0 beats per second. How...
  25. G

    Relativistic Doppler shift Problem

    A distant galaxy is moving away from us at a speed of 1.85x10^7m/s. Starting from the formula for the doppler shifted frequency, derive a formula for the change in wavelength and hence calculate the fractional redshift (λ'-λ₀)/λ₀ in the light from the galaxy. I'm pretty confused at the moment...
  26. C

    Doppler shift above speed of sound.

    Homework Statement A source and an observer are each traveling at 0.52 times the speed of sound. The source emits sound waves at 1.2 kHz. (a) Find the observed frequency (in kHz) if the source and observer are moving toward each other. (b) Find the observed frequency (in Hz) if the...
  27. S

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  28. T

    Doppler Shift: Same Direction, Same Velocity?

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  29. A

    Question on Relativistic Doppler Shift

    I have a quick relativity question. Say an observer is moving at a relativistic velocity with respect to some light source that emits light at one particular frequency (the observer's path does not intersect the emitter). At the point of closest approach, will light from the emitter be Doppler...
  30. B

    Doppler shift formula and the assumptions behind it

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  31. S

    Doppler Shift in Binary stars?

    I know that in spectroscopic Binaries, you can observe wavelength shifts in each star. But how do you determine the total radial velocity of this system alltogether, and how do you find each star's radial velocity?
  32. K

    Is there a maximum doppler shift?

    I was playing around with a thought experiment where an observer is moving towards a light source at a speed infinitesimally less than C and it seems like, for any given wavelength, the maximum possible Doppler shift is 1/2. for example near infrared light with a wavelength of 800 nm would be...
  33. Q

    Is the Doppler shift an independent principle?

    Is the Doppler shift an independent principle of wave mechanics? Or we can deduce it from other principles of wave mechanics? The article [1] gives an analogy of throwing and receiving balls. But it may be inappropriate. We are discussing wave mechanics? Why bother an analogy of balls/particles...
  34. F

    Astronomy and the Relativistic Doppler Shift

    Homework Statement The hydrogen atoms in a star are also moving at high velocity because of the random motions caused by their high temperature. As a result, each atom is Doppler shifted a little bit differently, leading to a finite width of each spectral line, such as the 656.46-nm line we...
  35. P

    What is the Period of the Sun's Rotation Based on Doppler Shift of Light?

    I have to calculate the suns period time, when given the following information; "The H_{alpha} line has the wavelength \lambda_0 = 656.1~nm . Measuring this spectrum from opposite sites of the suns equator, shows that there is a difference between that is \Delta \lambda=9\times 10^{-12}~m ...
  36. M

    Deriving Doppler Shift Using Spacetime Diagram

    Alright, I'm trying to derive the dopper shift using a spacetime diagram (see attached). If we model light pulses then we can derive the distance between the pulses in time, and hence the doppler shift... right? So, if we make some light pulses along some sort of time event in the x, cT frame...
  37. N

    Can a galaxy have a recession velocity greater than the speed of light?

    Hi all. I was reading: http://www.astro.ucla.edu/~wright/doppler.htm but I'm failing to understand this part: My understanding is that a galaxy cannot move faster than c (the speed of light). Why then could a galaxy moving close to c have a recession velocity greater than the speed of light...
  38. Link

    How to calculate relative doppler shift

    I am to measure the rotational velocity of Io relative to Jupiter, and will do so using a spectrograph. I will measure the frequency change of a specific mineral emmision band in the spectra, and then check how much it has shifted from its original wavelenght with a table. Then I use the...
  39. D

    How Does the Doppler Shift Affect Light When Approaching a Source?

    do you get a doppler shift when your moving towards a light source? like, i know light gets redshifted with expanding space and gravity, but if light always approaches you at the same speed, how would frequency change there?
  40. R

    Relativistic doppler shift

    For the relativistic doppler shift: change in wavelength = (c - Vs) To / (1 - Vs ^2 /c^2)^1/2 where Vs is emitter velocity, c is speed of light and To is time. Suppose change in wavelength was equal to just 1 / (1 - Vs ^2 / c^2)^1/2 then (c - Vs) To = 1 c -Vs = 1 / To c = Vs + 1...
  41. F

    Doppler Shift Equation: How to Calculate Frequency of a Stationary Train

    A train moving toward a detector at 31m/s blows a 305-Hz horn. What frequency is detected by a statiory train? Using the equation f´= f(V + Vd/ V - Vs) The answer is supposed to be 340-Hz but I don't understand how to get it. Mind helping me out?
  42. I

    What is FOR ? doppler shift?

    What is "FOR"? doppler shift? What is "FOR"? I believe it an acronym having to do with the doppler shift? :confused:
  43. C

    Photon Doppler Shift: Exploring the Theory

    Photon Doppler Shift? I am a practicing EE who has used the standard Doppler shift equation for thirty years in radar design; therefore, I am not disputing the correctness of the equation but the "explanation" that is so often given in textbooks. The general explanation always discusses...
  44. G

    Exploring the Relativistic Doppler Shift

    relativistic doppler shift I'm trying to show that this equation for the doppler shift for light: f' = [&radic;(1+(v/c))/&radic;(1-(v/c))] * f reduces to &Delta;f/f = -v/c for v<<c So I expanded (1+v/c)^(1/2) = 1 + v/(2c) and (1-v/c)^(1/2) = 1 - v/(2c) dropping higher order terms on the...
  45. S

    Doppler Shift: Deriving a Formula for Both Moving Objects

    My book derives two formulas for Doppler shift. One for when the source moves and one for when the observer moves. What about when both are moving? I tried deriving it myself... but I couldn't :( If you want, you could just give me a hint on how to derive it.
  46. C

    What is the Doppler shift equation for light?

    i've been having a tough time trying to solve the following problem. A pulsating star has a period of 3 sec as seen from the rest mass frame of the star. What is the period of the star as measured by an observer traveling 2.2e8 m/s with respect to the star? I assumed that it was simply...
  47. T

    Doppler shift and red/blue shift

    Suppose we have a weightless light source that is moving. Its output light will therefore undergo a Doppler shift. Now, if the lightsource had weight but were static, its light would undergo a red shift. If the light source had weight and were moving, would it undergo both a red shift and a...
  48. M

    Is Relativity the Key to Understanding Doppler Shift on a Moving Train?

    I’m on a train sitting next to an open window - it’s a bit stuffy - traveling towards a station. A siren is sounding at the station. As I travel toward the siren its pitch is higher that it would be if I were stood on the platform. Once I have passed the siren and I’m moving away, its pitch...
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