Redshift

red shiftzred-shiftred-shiftedredshiftsredshiftedhigh-redshiftspectral shifthigh redshiftRed shift observations in astronomy
In physics, redshift is a phenomenon where electromagnetic radiation (such as light) from an object undergoes an increase in wavelength.wikipedia
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Blueshift

blue shiftblue-shiftedblue-shift
The opposite of a redshift is a blueshift, where wavelengths shorten and energy increases.
A blueshift is any decrease in wavelength, with a corresponding increase in frequency, of an electromagnetic wave; the opposite effect is referred to as redshift.

Red

Redscolor redScarlet
The emitted light is not actually red; instead, the term refers to the human perception of longer wavelengths at the red end of the visible spectrum.
Astronomical objects that are moving away from the observer exhibit a Doppler red shift.

Electromagnetic radiation

electromagnetic waveelectromagnetic waveselectromagnetic
In physics, redshift is a phenomenon where electromagnetic radiation (such as light) from an object undergoes an increase in wavelength.
Spectroscopy is also used in the determination of the distance of a star, using the red shift.

Big Bang

Big Bang Theorybig-bangbirth
However, in many contexts, such as black holes and Big Bang cosmology, redshifts must be calculated using general relativity.
In 1929, from analysis of galactic redshifts, Edwin Hubble concluded that galaxies are drifting apart; this is important observational evidence consistent with the hypothesis of an expanding universe.

Doppler effect

Dopplerdoppler shiftDoppler shifts
1) Objects move apart (or closer together) in space. This is an example of the Doppler effect.
The Doppler effect for electromagnetic waves such as light is of great use in astronomy and results in either a so-called redshift or blueshift.

Cosmology

cosmologistcosmologicalcosmologies
2) Space itself expands, causing objects to become separated without changing their positions in space. This is known as cosmological redshift. All sufficiently distant light sources (generally more than a few million light years away) show redshift corresponding to the rate of increase in their distance from Earth, known as Hubble's Law.
Thus the Big Bang model was proposed by the Belgian priest Georges Lemaître in 1927 which was subsequently corroborated by Edwin Hubble's discovery of the red shift in 1929 and later by the discovery of the cosmic microwave background radiation by Arno Penzias and Robert Woodrow Wilson in 1964.

Hydrogen spectral series

hydrogen lineshydrogen spectrumseries
The spectrum of originally featureless light shone through hydrogen will show a signature spectrum specific to hydrogen that has features at regular intervals.
The spectral series are important in astronomical spectroscopy for detecting the presence of hydrogen and calculating red shifts.

William Huggins

Sir William HugginsHugginsHuggins, Sir William
In 1868, British astronomer William Huggins was the first to determine the velocity of a star moving away from the Earth by this method.
With observations of Sirius showing a redshift in 1868, Huggins hypothesized that a radial velocity of the star could be computed.

Hippolyte Fizeau

FizeauA. H. L. FizeauArmand Hippolyte L. Fizeau
The first Doppler redshift was described by French physicist Hippolyte Fizeau in 1848, who pointed to the shift in spectral lines seen in stars as being due to the Doppler effect.
In 1848, he predicted the redshifting of electromagnetic waves.

Expansion of the universe

expanding universeexpandingexpansion of space
2) Space itself expands, causing objects to become separated without changing their positions in space. This is known as cosmological redshift. All sufficiently distant light sources (generally more than a few million light years away) show redshift corresponding to the rate of increase in their distance from Earth, known as Hubble's Law.
In 1929, Edwin Hubble discovered that light from remote galaxies was redshifted; i.e. the more remote galaxies were, the more shifted was the light coming from them.

General relativity

general theory of relativityrelativitygeneral relativity theory
However, in many contexts, such as black holes and Big Bang cosmology, redshifts must be calculated using general relativity. 3) Gravitational redshift is a relativistic effect observed due to strong gravitational fields, which distort spacetime and exert a force on light and other particles.
Light sent down into a gravity well is blueshifted, whereas light sent in the opposite direction (i.e., climbing out of the gravity well) is redshifted; collectively, these two effects are known as the gravitational frequency shift.

Vesto Slipher

V.M. SlipherSlipherSlipher, Vesto Melvin
Beginning with observations in 1912, Vesto Slipher discovered that most spiral galaxies, then mostly thought to be spiral nebulae, had considerable redshifts.
In 1912, he was the first to observe the shift of spectral lines of galaxies, making him the discoverer of galactic redshifts.

Hubble's law

Hubble constantcosmological redshiftHubble parameter
2) Space itself expands, causing objects to become separated without changing their positions in space. This is known as cosmological redshift. All sufficiently distant light sources (generally more than a few million light years away) show redshift corresponding to the rate of increase in their distance from Earth, known as Hubble's Law. Subsequently, Edwin Hubble discovered an approximate relationship between the redshifts of such "nebulae" and the distances to them with the formulation of his eponymous Hubble's law.
1) Objects observed in deep space—extragalactic space, 10 megaparsecs (Mpc) or more—are found to have a redshift, interpreted as a relative velocity away from Earth;

Relativistic Doppler effect

transverse Doppler effectDoppler effectDoppler effect for electromagnetic waves
A complete derivation of the effect can be found in the article on the relativistic Doppler effect.
Astronomers know of three sources of redshift/blueshift: Doppler shifts; gravitational redshifts (due to light exiting a gravitational field); and cosmological expansion (where space itself stretches).

Event horizon

event horizonshorizoncosmic event horizon
However, it is significant near a black hole, and as an object approaches the event horizon the red shift becomes infinite.
Likewise, any object approaching the horizon from the observer's side appears to slow down and never quite pass through the horizon, with its image becoming more and more redshifted as time elapses.

Tired light

tired-light
Alternative hypotheses and explanations for redshift such as tired light are not generally considered plausible.
Tired light is a class of hypothetical redshift mechanisms that was proposed as an alternative explanation for the redshift-distance relationship.

Ives–Stilwell experiment

Ives and StillwellIves and Stilwell (1938)Ives–Stilwell
This phenomenon was first observed in a 1938 experiment performed by Herbert E. Ives and G.R. Stilwell, called the Ives–Stilwell experiment.
Under special relativity, the two frequencies will also include an additional Lorentz factor redshift correction represented by the TDE formula:

Astronomical spectroscopy

spectrumspectroscopicspectra
Redshifts are also seen in the spectroscopic observations of astronomical objects.
Because of the Doppler effect, objects moving towards us are blueshifted, and objects moving away are redshifted.

Edwin Hubble

HubbleEdwin P. HubbleEdwin Powell Hubble
Subsequently, Edwin Hubble discovered an approximate relationship between the redshifts of such "nebulae" and the distances to them with the formulation of his eponymous Hubble's law.
In 1929, in his first published paper, Hubble examined the relation between distance and redshift of galaxies.

Pound–Rebka experiment

first successful laboratory measurementPound & Rebka (1959)Pound and Rebka
The effect is very small but measurable on Earth using the Mössbauer effect and was first observed in the Pound–Rebka experiment.
It is a gravitational redshift experiment, which measures the redshift of light moving in a gravitational field, or, equivalently, a test of the general relativity prediction that clocks should run at different rates at different places in a gravitational field.

Infrared

IRnear-infraredinfra-red
, it would be brightest in the infrared rather than at the yellow-green color associated with the peak of its blackbody spectrum, and the light intensity will be reduced in the filter by a factor of four,
Infrared astronomy uses sensor-equipped telescopes to penetrate dusty regions of space such as molecular clouds, detect objects such as planets, and to view highly red-shifted objects from the early days of the universe.

Visible spectrum

visiblevisible lightspectrum
The emitted light is not actually red; instead, the term refers to the human perception of longer wavelengths at the red end of the visible spectrum.
The shifting of spectral lines can be used to measure the Doppler shift (red shift or blue shift) of distant objects.

Hydrogen

HH 2 hydrogen gas
A very common atomic element in space is hydrogen.
The large amount of neutral hydrogen found in the damped Lyman-alpha systems is thought to dominate the cosmological baryonic density of the Universe up to redshift z=4.

Scale factor (cosmology)

scale factorcosmic scale factorscale factors
is the time-dependent cosmic scale factor
According to the Friedmann–Lemaître–Robertson–Walker metric which is used to model the expanding universe, if at the present time we receive light from a distant object with a redshift of z, then the scale factor at the time the object originally emitted that light is.

K correction

adjusted for redshiftsk-correctionkcorrect
(See K correction for more details on the photometric consequences of redshift.)
K correction is a correction to an astronomical object's magnitude (or equivalently, its flux) that allows a measurement of a quantity of light from an object at a redshift z to be converted to an equivalent measurement in the rest frame of the object.