Redshift
Redshift measures the stretching of light from moving or distant sources.
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 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, and by the wavelength ratio 1+z.
- field
- Physics, Astronomy, Cosmology
- known_for
- Increase in wavelength of electromagnetic radiation; key to measuring cosmic expansion
Lore & Background
He reported velocities for 15 spiral nebulae, all but three having recessional velocities.
Reader's Guide
Redshift is a fundamental concept in modern cosmology, providing the primary observational evidence for the expansion of the universe. The discovery of cosmological redshifts, combined with theoretical models from general relativity, marked a major breakthrough: the universe had a history and its expansion could be studied. Automated astronomical redshift surveys are an important tool for learning about the large-scale structure of the universe. Examples of strong redshifting include gamma rays perceived as X-rays, or visible light perceived as radio waves. Subtler redshifts are used in terrestrial technologies such as Doppler radar and radar guns. Gravitational waves, traveling at the speed of light, are subject to the same redshift phenomena. Other physical processes like scattering can shift frequency but are not generally referred to as astronomical redshift.
Did You Know?
- Fritz Zwicky proposed a 'tired light' model for cosmological redshifts, but it was largely ruled out by timescale stretch observations in type Ia supernovae.
- In the 1960s, quasars were initially thought to be unusual stars because they appeared as very blue point sources, but redshift data showed they were very powerful distant objects.
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