What is Redshift: Definition and 384 Discussions

In physics, a redshift is an increase in the wavelength, and corresponding decrease in the frequency and photon energy, of electromagnetic radiation (such as light). The opposite change, a decrease in wavelength and simultaneous increase in frequency and energy, is known as a negative redshift, or blueshift. The terms derive from the colours red and blue which form the extremes of the visible light spectrum.
In astronomy and cosmology, the three main causes of electromagnetic redshift are

The radiation travels between objects which are moving apart ("relativistic" redshift, an example of the relativistic Doppler effect)
The radiation travels towards an object in a weaker gravitational potential, i.e. towards an object in less strongly curved (flatter) spacetime (gravitational redshift)
The radiation travels through expanding space (cosmological redshift). The observation that all sufficiently distant light sources show redshift corresponding to their distance from Earth is known as Hubble's law.Relativistic, gravitational, and cosmological redshifts can be understood under the umbrella of frame transformation laws. Gravitational waves, which also travel at the speed of light, are subject to the same redshift phenomena.
Examples of strong redshifting are a gamma ray perceived as an X-ray, or initially visible light perceived as radio waves. Subtler redshifts are seen in the spectroscopic observations of astronomical objects, and are used in terrestrial technologies such as Doppler radar and radar guns.
Other physical processes exist that can lead to a shift in the frequency of electromagnetic radiation, including scattering and optical effects; however, the resulting changes are distinguishable from (astronomical) redshift and are not generally referred to as such (see section on physical optics and radiative transfer).
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 >1 for redshifts, <1 for blueshifts).

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  1. G

    I Diffraction Redshift and Emission Theory

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  2. E

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  3. J

    An argument that massive particles don't redshift?

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  4. J

    Onset of Universe acceleration

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  5. J

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  6. J

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  7. P

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  8. U

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  10. stevebd1

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  11. J

    Behavior of redshift over time

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  12. P

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  13. C

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  14. U

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  15. wabbit

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  16. Q

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  17. F

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  18. D

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  19. I

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  21. U

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  22. R

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  23. bitznbitez

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  24. 2

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  25. S

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  26. J

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  27. T

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  29. avito009

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  30. Wes Tausend

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  31. M

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  32. A

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  33. ellipsis

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  34. aditya ver.2.0

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  35. R

    Gravitation Redshift for very dense stars

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  36. E

    Gravitational redshift with time dilation?

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  37. M

    Understanding Redshift: Mathias' 15-Year-Old Query

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  38. C

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  39. TumblingDice

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  40. B

    Calculating Redshift for Objects in the Universe: A Step-by-Step Guide

    We know that z redshift (+1) ir the ratio between the observed and emitted wavelength. Could you tell me, in practice, how you can you find z for a star? or can you give me a link where a particular case is explained in detail? Any object (star, (proto-)galaxy,quasar) emits EMR in a wide...
  41. K

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  42. Q

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  43. Matterwave

    Cosmological Redshift: Electron Energy Loss in Expanding Universe?

    So I have been thinking. Light gets redshifted because of the cosmological expansion of the Universe. This would mean that other, material particles, should get "cosmologically redshifted" as well right? So, for example, if an electron were flying towards us from some distant galaxy (and we...
  44. P

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  45. S

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  46. tom.stoer

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  47. H

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  48. B

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  49. WannabeNewton

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  50. T

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