Relativistic Doppler effect

The relativistic Doppler effect is the change in <a href="/facts/Frequency/QUSbPaW8">frequency</a>, <a href="/facts/Wavelength/kcJU0ymz">wavelength</a> and <a href="/facts/Amplitude/aEckuXJM">amplitude</a> of light, caused by the relative motion of the source and the observer (as in the classical <a href="/facts/Doppler_effect/bzrK1BKf">Doppler effect</a>, first proposed by Christian Doppler in 1842), when taking into account effects described by the <a href="/facts/Special_relativity/vsFFc63E">special theory of relativity</a>. 
The relativistic Doppler effect is different from the non-relativistic <a href="/facts/Doppler_effect/bzrK1BKf">Doppler effect</a> as the equations include the <a href="/facts/Time_dilation/fYj7FYbK">time dilation</a> effect of <a href="/facts/Special_relativity/vsFFc63E">special relativity</a> and do not involve the medium of propagation as a reference point. They describe the total difference in observed frequencies and possess the required <a href="/facts/Lorentz_symmetry/K5AEuGKg">Lorentz symmetry</a>.
Astronomers know of three sources of <a href="/facts/Redshift/Qfl4VjDF">redshift</a>/<a href="/facts/Blueshift/v8XBtGKH">blueshift</a>: Doppler shifts; <a href="/facts/Gravitational_redshift/cEFgB3Ns">gravitational redshifts</a> (due to light exiting a gravitational field); and <a href="/facts/Cosmological_expansion/f6Uvt79B">cosmological expansion</a> (where space itself stretches). This article concerns itself only with Doppler shifts.

Relativistic Doppler effect open-in-new

Relativistic Doppler effect