Editing Redshift (section)

==Concept==
[[File:High-redshift galaxy candidates in the Hubble Ultra Deep Field 2012.jpg|thumb|High-redshift galaxy candidates in the [[Hubble Ultra Deep Field]], 2012<ref>{{cite news|title=Hubble census finds galaxies at redshifts 9 to 12|url=https://esahubble.org/news/heic1219/|access-date=13 December 2012|newspaper=ESA/Hubble Press Release}}</ref> ]]

Using a telescope and a [[spectrometer]], the variation in intensity of star light with frequency can be measured. The resulting spectrum can be compared to the spectrum from hot gases expected in stars, such as [[hydrogen]], in a laboratory on Earth. As illustrated with the idealized spectrum in the top-right, to determine the redshift, features in the two spectra such as [[spectral line|absorption lines]], [[spectral line|emission lines]], or other variations in light intensity<!--Don't link to disambiguation page--> may be shifted. 

Redshift (and blueshift) may be characterized by the relative difference between the observed and emitted wavelengths (or frequency) of an object. In astronomy, it is customary to refer to this change using a [[dimensionless quantity]] called {{math|''z''}}. If {{math|''λ''}} represents wavelength and {{math|''f''}} represents frequency (note, {{math|''λf'' {{=}} ''c''}} where {{math|''c''}} is the [[speed of light]]), then {{math|''z''}} is defined by the equations:<ref>For a tutorial on how to define and interpret large redshift measurements, see:<br />{{cite web
 | title=Extragalactic Redshifts
 | first=John
 | last=Huchra
 | publisher=Harvard-Smithsonian Center for Astrophysics
 | website=NASA/IPAC Extragalactic Database
 | url=http://ned.ipac.caltech.edu/help/zdef.html
 | access-date=2023-03-16
 | archive-date=2013-12-22
 | archive-url=https://web.archive.org/web/20131222052715/http://ned.ipac.caltech.edu/help/zdef.html
 
 }}</ref>

{| class="wikitable" style="margin:auto;"
|+ Calculation of redshift, <math>z</math>
!Based on wavelength!!Based on frequency
|- align=center
| <math>z = \frac{\lambda_{\mathrm{obsv}} - \lambda_{\mathrm{emit}}}{\lambda_{\mathrm{emit}}}</math>
| <math>z = \frac{f_{\mathrm{emit}} - f_{\mathrm{obsv}}}{f_{\mathrm{obsv}}}</math>
|- align=center
| <math>1+z = \frac{\lambda_{\mathrm{obsv}}}{\lambda_{\mathrm{emit}}}</math>
| <math>1+z = \frac{f_{\mathrm{emit}}}{f_{\mathrm{obsv}}}</math>
|}

[[Doppler effect]] blueshifts ({{math|''z'' < 0}}) are associated with objects approaching (moving closer to) the observer with the light shifting to greater [[energy|energies]]. Conversely, Doppler effect redshifts ({{math|''z'' > 0}}) are associated with objects receding (moving away) from the observer with the light shifting to lower energies. Likewise, gravitational blueshifts are associated with light emitted from a source residing within a weaker [[gravitational field]] as observed from within a stronger gravitational field, while gravitational redshifting implies the opposite conditions.