###### Answer: Both

Relativistic Doppler shift for the longitudinal case with source and receiver moving directly towards or away from each other is often derived as if it were the classical phenomenon but modified by the addition of a time dilation term. This is the approach employed in first-year physics or mechanics textbooks such as those by Feynman or Morin. Following this approach towards deriving the relativistic longitudinal Doppler effect assume the receiver and the source are moving away from each other with a relative speed ${\displaystyl…

Relativistic Doppler shift for the longitudinal case with source and receiver moving directly towards or away from each other is often derived as if it were the classical phenomenon but modified by the addition of a time dilation term. This is the approach employed in first-year physics or mechanics textbooks such as those by Feynman or Morin. Following this approach towards deriving the relativistic longitudinal Doppler effect assume the receiver and the source are moving away from each other with a relative speed ${\displaystyle v\ }$ as measured by an observer on the receiver or the source (The sign convention adopted here is that ${\displaystyle v\ }$ is negative if the receiver and the source are moving towards each other). Consider the problem in the reference frame of the source. Suppose one wavefront arrives at the receiver. The next wavefront is then at a distance ${\displaystyle \lambda _{s}=c/f_{s}\ }$ away from the receiver (where ${\displaystyle \lambda _{s}\ }$ is the wavelength ${\displaystyle f_{s}\ }$ is the frequency of the waves that the source emits and ${\displaystyle c\ }$ is the speed of light). The wavefront moves with speed ${\displaystyle c\ }$ but at the same time the receiver moves away with speed ${\displaystyle v}$ during a time ${\displaystyle t_{s}=1/f_{s}=\lambda _{s}/c}$ so ${\displaystyle f_{r s}=1/t_{r s}=f_{s}(1-\beta ).}$ Thus far the equations have been identical to those of the classical Doppler effect with a stationary source and a moving receiver. However due to relativistic effects clocks on the receiver are time dilated relative to clocks at the source: ${\displaystyle t_{r}=t_{r s}/\gamma }$ where ${\textstyle \gamma =1/{\sqrt {1-\beta ^{2}}}}$ is the L…

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 …

The transverse Doppler effect is observed during the short moment when the vector c’ is aligned precisely perpendicularly with respect to the velocity vector v. Bradley’s theorem then leads to a rectangular vector triangle the hypotenuse of which is c. From the proportionality relation f ‘ / f = c’ / c (where f ‘ is the Doppler shifted frequency of oscillation) and the Pythagorean law follows then the well …

Doppler effect – Wikipedia

Relativistic Doppler effect – Wikipedia

Relativistic Doppler effect – Wikipedia

Doppler effect – Wikipedia

Über das farbige Licht der Doppelsterne und einiger anderer Gestirne des Himmels is a treatise by Christian Doppler (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 .The original Germa…