Redshift
relative increase in wavelength of electromagnetic radiation in the emission spectrum of astronomical objects
In physics, a redshift is an increase in the wavelength, or equivalently, a decrease in the frequency, of electromagnetic radiation (such as light). The opposite change, a decrease in wavelength and increase in frequency and energy, is known as a blueshift.
Three forms of redshift occur in astronomy and cosmology: Doppler redshifts due to the relative motions of radiation sources, gravitational redshift as radiation escapes from gravitational potentials, and cosmological redshifts caused by the universe expanding. The value of a redshift is often denoted by the letter z, corresponding to the fractional change in wavelength (positive for redshifts, negative for blueshifts), and by the wavelength ratio 1 + z (which is greater than 1 for redshifts and less than 1 for blueshifts). Automated astronomical redshift surveys are an important tool for learning about the large-scale structure of the universe. Redshift and blueshift can also be related to photon energy and, via Planck's law, to a corresponding blackbody temperature.
Examples of strong redshifting are a gamma ray perceived as an X-ray, or initially visible light perceived as radio waves. The initial 3000 kelvin (K) radiation from the Big Bang has redshifted far down to become the 3 K cosmic microwave background. Subtler redshifts are seen in the spectroscopic observations of astronomical objects, and are used in terrestrial technologies such as Doppler radar and radar guns.
Gravitational waves, which also travel at the speed of light, are subject to the same redshift phenomena.
“Redshift” enters the record as relative increase in wavelength of electromagnetic radiation in the emission spectrum of astronomical objects. Crown Archives preserves that source wording while asking what Redshift, relative and increase can confirm, complicate or overturn.
Why this record matters
“Redshift” is worth following because a concise public description often conceals a longer documentary argument. Here, Redshift, relative and increase provides the most credible route into that argument.
The citation trail is more important than the brevity of the summary: it shows where individual claims can be examined in context. The source revision retrieved here is dated Sep 7, 2026. The linked authority identifier is Q76250. The Library of Congress control number is sh85112092. 1 of 1 selected statements include explicit references; 0 carry qualifiers and 0 use preferred rank.
A concise general-reference account can conceal disagreements about scope, terminology or the weight assigned to individual sources. The lead is largely declarative, so disagreement and counter-evidence require a deliberate search beyond the opening account. Authority statements aid reconciliation but still require their own references, qualifiers and ranks to be checked.
How to read it
Use the entry as an orientation point, then follow its citations and revision history. Names, dates and institutional relationships should be checked against the original record.
- Subject orientation
- Search vocabulary
- Locating named sources
The closest primary source, responsible institution and strongest cited specialist reference.
Three-step research path
- Establish the record: confirm the title “Redshift”, its source revision and the description used here.
- Expand the search: follow Redshift primary sources, Redshift archive and Redshift research across catalogues and specialist indexes.
- Test the account: compare the strongest cited source with the responsible institution’s current record and note any disagreement.
Questions for further research
- Which source most directly establishes the central claim about “Redshift”?
- Which cited source is closest to the event, object or claim?
- Which institution is responsible for the underlying evidence?
Search terms from this dossier
This entry incorporates text from “Redshift” on English Wikipedia. Contributors are listed in the page history. Text is available under the Creative Commons Attribution-ShareAlike 4.0 License. Selected authority identifiers and statements are retrieved from Wikidata under CC0; their references and qualifiers remain part of the verification path.