Editing Doppler effect (section)

===Astronomy===
{{Main|Relativistic Doppler effect}}

[[Image:Redshift.svg|thumb|upright|[[Redshift]] of [[spectral line]]s in the [[optical spectrum]] of a supercluster of distant galaxies (right), as compared to that of the Sun (left)]]

The [[Relativistic Doppler effect|Doppler effect for electromagnetic waves]] such as light is of widespread use in [[astronomy]] to measure the speed at which [[star]]s and [[galaxy|galaxies]] are approaching or receding from us, resulting in so called [[blueshift]] or [[redshift]], respectively. This may be used to detect if an apparently single star is, in reality, a close [[Binary star|binary]], to measure the rotational speed of stars and galaxies, or to [[Doppler spectroscopy|detect exoplanets]]. This effect typically happens on a very small scale; there would not be a noticeable difference in visible light to the unaided eye.<ref>{{cite web |url=http://www.astro.ucla.edu/~wright/doppler.htm|title=Doppler Shift| website=astro.ucla.edu}}</ref>
The use of the Doppler effect in astronomy depends on knowledge of precise frequencies of [[spectral line|discrete lines]] in the [[electromagnetic spectroscopy|spectra]] of stars.

Among the [[List of nearest stars|nearby stars]], the largest [[radial velocities]] with respect to the [[Sun]] are +308&nbsp;km/s ([[BD-15°4041]], also known as LHS 52, 81.7 light-years away) and −260&nbsp;km/s ([[Woolley 9722]], also known as Wolf 1106 and LHS 64, 78.2 light-years away). Positive radial speed means the star is receding from the Sun, negative that it is approaching.

The relationship between the [[Redshift#Expansion of space|expansion of the universe]] and the Doppler effect is not simple matter of the source moving away from the observer.<ref name="Peacock">{{cite arXiv|eprint=0809.4573|class=astro-ph|author=JA Peacock|title=A diatribe on expanding space|date=2008}}</ref><ref name="Hogg">{{cite journal |author=Bunn |first1=E. F. |last2=Hogg |first2=D. W. |year=2009 |title=The kinematic origin of the cosmological redshift |journal=American Journal of Physics |volume=77 |issue=8 |pages=688–694 |arxiv=0808.1081 |bibcode=2009AmJPh..77..688B |doi=10.1119/1.3129103 |s2cid=1365918}}</ref> In cosmology, the redshift of expansion is considered separate from redshifts due to gravity or Doppler motion.<ref>{{cite book |last=Harrison |first=Edward Robert  |date= 2000 |title=Cosmology: The Science of the Universe |publisher=Cambridge University Press |edition=2nd |url=https://books.google.com/books?id=-8PJbcA2lLoC&pg=PA315|pages=306''ff'' |isbn=978-0-521-66148-5 }}</ref>

Distant galaxies also exhibit [[peculiar motion]] distinct from their cosmological recession speeds. If redshifts are used to determine distances in accordance with [[Hubble's law]], then these peculiar motions give rise to [[redshift-space distortions]].<ref>An excellent review of the topic in technical detail is given here: {{cite journal|last1=Percival|first1=Will| last2=Samushia|first2=Lado| last3=Ross|first3=Ashley|last4=Shapiro|first4=Charles|last5=Raccanelli|first5=Alvise|year= 2011 |title=Review article: Redshift-space distortions|journal=Philosophical Transactions of the Royal Society|volume=369|issue=1957|pages=5058–67| doi=10.1098/rsta.2011.0370|pmid=22084293|bibcode=2011RSPTA.369.5058P|doi-access=free}}</ref>