Editing Relativistic Doppler effect (section)

==Visualization==
[[File:Compare01.jpg|thumb|300px|Figure 8. Comparison of the relativistic Doppler effect (top) with the non-relativistic effect (bottom).]]
Fig.&nbsp;8 helps us understand, in a rough qualitative sense, how the relativistic Doppler effect and [[relativistic aberration]] differ from the non-relativistic [[Doppler effect]] and non-relativistic [[aberration of light]]. Assume that the observer is uniformly surrounded in all directions by yellow stars emitting monochromatic light of 570&nbsp;nm. The arrows in each diagram represent the observer's velocity vector relative to its surroundings, with a magnitude of 0.89&nbsp;''c''. 
* In the relativistic case, the light ahead of the observer is blueshifted to a wavelength of 137&nbsp;nm in the far ultraviolet, while light behind the observer is redshifted to 2400&nbsp;nm in the short wavelength infrared. Because of the relativistic aberration of light, objects formerly at right angles to the observer appear shifted forwards by 63°.
* In the non-relativistic case, the light ahead of the observer is blueshifted to a wavelength of 300&nbsp;nm in the medium ultraviolet, while light behind the observer is redshifted to 5200&nbsp;nm in the intermediate infrared. Because of the aberration of light, objects formerly at right angles to the observer appear shifted forwards by 42°. 
* In both cases, the monochromatic stars ahead of and behind the observer are Doppler-shifted towards invisible wavelengths. If, however, the observer had eyes that could see into the ultraviolet and infrared, he would see the stars ahead of him as brighter and more closely clustered together than the stars behind, but the stars would be far brighter and far more concentrated in the relativistic case.<ref name="Savage1999">{{cite journal |last1=Savage |first1=C. M. |last2=Searle |first2=A. C. |title=Visualizing Special Relativity |journal=The Physicist |date=1999 |volume=36 |issue=141 |url=http://www.anu.edu.au/Physics/Searle/paper2/paper2.pdf |archive-url=https://web.archive.org/web/20080803005209/http://www.anu.edu.au/Physics/Searle/paper2/paper2.pdf |url-status=dead |archive-date=2008-08-03 |access-date=17 October 2018}}</ref>

Real stars are not monochromatic, but emit a range of wavelengths approximating a [[black body]] distribution. It is not necessarily true that stars ahead of the observer would show a bluer color. This is because the whole spectral energy distribution is shifted. At the same time that visible light is blueshifted into invisible ultraviolet wavelengths, infrared light is blueshifted into the visible range. Precisely what changes in the colors one sees depends on the physiology of the human eye and on the spectral characteristics of the light sources being observed.<ref name="Brandeker">{{cite web |last1=Brandeker |first1=Alexis |title=What would a relativistic interstellar traveller see? |url=http://www.math.ucr.edu/home/baez/physics/Relativity/SR/Spaceship/spaceship.html |website=Physics FAQ |publisher=Math Department, University of California, Riverside |access-date=17 October 2018 |archive-date=7 May 2021 |archive-url=https://web.archive.org/web/20210507132207/https://math.ucr.edu/home/baez/physics/Relativity/SR/Spaceship/spaceship.html |url-status=dead }}</ref><ref name="Kraus2000">{{cite journal |last1=Kraus |first1=U. |title=Brightness and color of rapidly moving objects: The visual appearance of a large sphere revisited |journal=Am. J. Phys. |date=2000 |volume=68 |issue=1 |pages=56–60 |url=https://www.spacetimetravel.org/sphere/sphere.pdf |access-date=17 October 2018|doi=10.1119/1.19373 |bibcode=2000AmJPh..68...56K }}</ref>