Editing Relativistic Doppler effect (section)

{{Special relativity sidebar}}
{{short description|Scientific phenomenon}}
[[Image:Velocity0 70c.jpg|thumb|right|Figure 1. A source of light waves moving to the right, relative to observers, with velocity 0.7''c''. The frequency is higher for observers on the right, and lower for observers on the left.]]
The '''relativistic Doppler effect''' is the change in [[frequency]], [[wavelength]] and [[amplitude]]<ref>{{cite book |title=Relativistic Electron Mirrors: from High Intensity Laser–Nanofoil Interactions |author1=Daniel Kiefer |edition=illustrated |publisher=Springer |year=2014 |isbn=978-3-319-07752-9 |page=22 |url=https://books.google.com/books?id=qdYkBAAAQBAJ}} [https://books.google.com/books?id=qdYkBAAAQBAJ&pg=PA22 Extract of page 22]</ref> of light, caused by the relative motion of the source and the observer (as in the classical [[Doppler effect]], first proposed by Christian Doppler in 1842<ref>{{Cite web |url=https://pubs.aip.org/physicstoday/article/73/3/30/850595/The-fall-and-rise-of-the-Doppler-effectThe |title=The Fall and Rise of the Doppler Effect ... |last=Nolte |first=David |date=2020-03-01 |website=pubs.aip.org/physicstoday |access-date=2024-11-02}}</ref>), when taking into account effects described by the [[special relativity|special theory of relativity]]. 

The relativistic Doppler effect is different from the non-relativistic [[Doppler effect]] as the equations include the [[time dilation]] effect of [[special relativity]] and do not involve the medium of propagation as a reference point. They describe the total difference in observed frequencies and possess the required [[Lorentz symmetry]].

Astronomers know of three sources of [[redshift]]/[[blueshift]]: Doppler shifts; [[gravitational redshift]]s (due to light exiting a gravitational field); and [[cosmological expansion]] (where space itself stretches). This article concerns itself only with Doppler shifts.