Absorption lines in the optical spectrum of a supercluster of distant galaxies (right), as compared to absorption lines in the optical spectrum of the Sun (left). Arrows indicate redshift. Wavelength increases up towards the red and beyond (frequency decreases).

Redshift and blue shift

In physics and astronomy, redshift occurs when the electromagnetic radiation, usually visible light, that is emitted from or reflected off an object is shifted towards the (less energetic) red end of the electromagnetic spectrum. More generally, redshift is defined as an increase in the wavelength of electromagnetic radiation received by a detector compared with the wavelength emitted by the source. This increase in wavelength corresponds to a decrease in the frequency of the electromagnetic radiation. Conversely, a decrease in wavelength is called blue shift. Bathochromic shift is a change of spectral band position in the absorption, reflectance, transmittance, or emission spectrum of a molecule to a longer wavelength (lower frequency). ... Redshift or red shift can refer to: // Redshift, light waves that come from the neubla Red shift, an informal term for a bathochromic shift RedShift (planetarium software), planetarium software created by Maris Multimedia Redshift (theory), techno-economic theory segmenting technology markets as either over or under-served by Moores... Image File history File links Redshift. ... Image File history File links Redshift. ... A spectral line is a dark or bright line in an otherwise uniform and continuous spectrum, resulting from an excess or deficiency of photons in a narrow frequency range, compared with the nearby frequencies. ... Visible light redirects here. ... A magnet levitating above a high-temperature superconductor demonstrates the Meissner effect. ... For other uses, see Astronomy (disambiguation). ... This box:      Electromagnetic (EM) radiation is a self-propagating wave in space with electric and magnetic components. ... The optical spectrum (light or visible spectrum) is the portion of the electromagnetic spectrum that is visible to the human eye. ... Although some radiations are marked as N for no in the diagram, some waves do in fact penetrate the atmosphere, although extremely minimally compared to the other radiations The electromagnetic (EM) spectrum is the range of all possible electromagnetic radiation. ... For other uses, see Wavelength (disambiguation). ... This box:      Electromagnetic (EM) radiation is a self-propagating wave in space with electric and magnetic components. ... In physics, emission is the process by which the energy of a photon is released by another entity, for example, by an atom whose valence electrons make a transition between two electronic energy levels. ... For other uses, see Frequency (disambiguation). ... This box:      Electromagnetic (EM) radiation is a self-propagating wave in space with electric and magnetic components. ... Blue shift is the opposite of redshift, the latter being much more noted due to its importance to modern astronomy. ...

Any increase in wavelength is called "redshift", even if it occurs in electromagnetic radiation of non-optical wavelengths, such as gamma rays, x-rays and ultraviolet. This nomenclature might be confusing since, at wavelengths longer than red (e.g., infrared, microwaves, and radio waves), redshifts shift the radiation away from the red wavelengths. This article is about electromagnetic radiation. ... In the NATO phonetic alphabet, X-ray represents the letter X. An X-ray picture (radiograph) taken by Röntgen An X-ray is a form of electromagnetic radiation with a wavelength approximately in the range of 5 pm to 10 nanometers (corresponding to frequencies in the range 30 PHz... For other uses, see Ultraviolet (disambiguation). ... For other uses, see Infrared (disambiguation). ... This article is about the type of Electromagnetic radiation. ... Radio waves are electromagnetic waves occurring on the radio frequency portion of the electromagnetic spectrum. ...

An observed redshift due to the Doppler effect occurs whenever a light source moves away from the observer, corresponding to the Doppler shift that changes the perceived frequency of sound waves. Although observing such redshifts, or complementary blue shifts, has several terrestrial applications (e.g., Doppler radar and radar guns),^[1] spectroscopic astrophysics uses Doppler redshifts to determine the movement of distant astronomical objects.^[2] This phenomenon was first predicted and observed in the 19th century as scientists began to consider the dynamical implications of the wave-nature of light. A source of waves moving to the left. ... This article is about audible acoustic waves. ... Doppler Effect Doppler radar uses the Doppler effect to measure the radial velocity of targets in the antennas directional beam. ... U.S. Army soldier uses a radar gun to catch speeding violators at Tallil Air Base, Iraq. ... High resolution spectrum of the Sun showing thousands of elemental absorption lines (fraunhofer lines). ... Surface waves in water This article is about waves in the most general scientific sense. ... For other uses, see Light (disambiguation). ...

Another cause of redshift is the expansion of the universe, which explains the observation that the redshifts of distant galaxies, quasars, and intergalactic gas clouds increase in proportion to their distance from the earth. This mechanism is a key feature of the Big Bang model of physical cosmology.^[3] This box:      The metric expansion of space is a key part of sciences current understanding of the universe, whereby spacetime itself is described by a metric which changes over time in such a way that the spatial dimensions grow or stretch as the universe gets older. ... For other uses, see Galaxy (disambiguation). ... This article is about the astronomical object. ... Intergalactic space is the physical space between galaxies. ... This article is about proportionality, the mathematical relation. ... For other uses, see Big Bang (disambiguation). ... This article is about the physics subject. ...

Gravitational redshift is observed if the receiver is located at higher gravitational potential than the source. The cause of gravitational redshift is the time dilation that occurs near massive objects, according to general relativity^[4] Graphic representing the gravitational redshift of a neutron star (not exact) In physics, light or other forms of electromagnetic radiation of a certain wavelength originating from a source placed in a region of stronger gravitational field (and which could be said to have climbed uphill out of a gravity well... In physics, gravitational potential is the measure of potential energy an object possesses due to its position in a gravitational field. ... Time dilation is the phenomenon whereby an observer finds that anothers clock which is physically identical to their own is ticking at a slower rate as measured by their own clock. ... For a generally accessible and less technical introduction to the topic, see Introduction to general relativity. ...

All three of these phenomena, whose wide range of instantiations are the focus of this article, can be understood under the umbrella of frame transformation laws, as described below. There exist numerous other mechanisms with different physical and mathematical descriptions that can lead to a shift in the frequency of electromagnetic radiation and whose action is generally not referred to as a "redshift", including scattering and optical effects (for more see section on physical optics and radiative transfer). Scattering is a general physical process whereby some forms of radiation, such as light, sound or moving particles, for example, are forced to deviate from a straight trajectory by one or more localized non-uniformities in the medium through which it passes. ... Physical Optics is the name of a high frequency approximation (short wavelength approximation) used in the electromagnetism of optics and radio. ...

History

The history of the subject began with the development in the 19th century of wave mechanics and the exploration of phenomena associated with the Doppler effect. The effect is named after Christian Andreas Doppler, who offered the first known physical explanation for the phenomenon in 1842.^[5] The hypothesis was tested and confirmed for sound waves by the Dutch scientist Christoph Hendrik Diederik Buys Ballot in 1845.^[6] Doppler correctly predicted that the phenomenon should apply to all waves, and in particular suggested that the varying colors of stars could be attributed to their motion with respect to the Earth.^[7] While this attribution turned out to be incorrect (stellar colors are indicators of a star's temperature, not motion), Doppler would later be vindicated by verified redshift observations. The wave equation is an important partial differential equation which generally describes all kinds of waves, such as sound waves, light waves and water waves. ... A source of waves moving to the left. ... Christian sex Doppler (November 29, 1803 _ March 17, 1853) was an American mathematician, most famous for the hypothesis of what is now known as the sex effect which causes the frequency of a wave to apparently change as its source moves toward sex or away from sex. ... This article is about audible acoustic waves. ... C.H.D. Buys Ballot Christophorus Henricus Diedericus Buys Ballot (also Christoph Heinrich Diedrich Buys Ballot) (October 10, 1817-February 3, 1890) Dutch chemist and meteorologist after whom Buys-Ballots law and the Buys Ballot table are called. ... Surface waves in water This article is about waves in the most general scientific sense. ... Color is an important part of the visual arts. ... This article is about the astronomical object. ... The CIE 1931 x,y chromaticity space, also showing the chromaticities of black-body light sources of various temperatures, and lines of constant correlated color temperature Color temperature is a characteristic of visible light that has important applications in photography, videography, publishing and other fields. ...

The first Doppler redshift was described in 1848 by French physicist Armand-Hippolyte-Louis Fizeau, who pointed to the shift in spectral lines seen in stars as being due to the Doppler effect. The effect is sometimes called the "Doppler-Fizeau effect". In 1868, British astronomer William Huggins was the first to determine the velocity of a star moving away from the Earth by this method.^[8] Armand Hippolyte Louis Fizeau Armand Hippolyte Louis Fizeau (September 23, 1819-1896), French physicist, was born in Paris. ... A spectral line is a dark or bright line in an otherwise uniform and continuous spectrum, resulting from an excess or deficiency of photons in a narrow frequency range, compared with the nearby frequencies. ... William Huggins Sir William Huggins, OM , FRS (February 7, 1824 – May 12, 1910) was a British astronomer. ...

In 1871, optical redshift was confirmed when the phenomenon was observed in Fraunhofer lines using solar rotation, about 0.1 Å in the red.^[9] In 1901 Aristarkh Belopolsky verified optical redshift in the laboratory using a system of rotating mirrors.^[10] Solar Fraunhofer lines In physics and optics, the Fraunhofer lines are a set of spectral lines named for the German physicist Joseph von Fraunhofer (1787--1826). ... Aristarkh Apollonovich Belopolsky (Аристарх Апполонович Белопольский) (July 13, 1854 (OS: July 1) – May 16, 1934) was a Russian astronomer. ...

The earliest occurrence of the term "red-shift" in print (in this hyphenated form), appears to be by American astronomer Walter S. Adams in 1908, where he mentions "Two methods of investigating that nature of the nebular red-shift".^[11] The word doesn't appear unhyphenated, perhaps indicating a more common usage of its German equivalent, Rotverschiebung, until about 1934 by Willem de Sitter.^[12] Walter Sydney Adams (December 20, 1876 – May 11, 1956) was an American astronomer. ... Willem de Sitter (May 6, 1872 – November 20, 1934) was a mathematician, physicist and astronomer. ...

Beginning with observations in 1912, Vesto Slipher discovered that most spiral nebulae had considerable redshifts.^[13] Subsequently, Edwin Hubble discovered an approximate relationship between the redshift of such "nebulae" (now known to be galaxies in their own right) and the distance to them with the formulation of his eponymous Hubble's law.^[14] These observations corroborated Alexander Friedman's 1922 work, in which he derived the famous Friedmann equations.^[15] They are today considered strong evidence for an expanding universe and the Big Bang theory.^[16] Vesto Melvin Slipher (November 11, 1875 – November 8, 1969) was an American astronomer. ... Spiral nebula is an old term for a spiral galaxy. ... Edwin Powell Hubble (November 20, 1889 – September 28, 1953) was an American astronomer. ... For other uses, see Galaxy (disambiguation). ... Distance is a numerical description of how far apart objects are at any given moment in time. ... This box:      Hubbles law is a statement in physical cosmology which states that the redshift in light coming from distant galaxies is proportional to their distance. ... Alexander Alexandrovich Friedman (June 16, 1888 – September 16, Russian cosmologist and mathematician. ... The Friedmann equations relate various cosmological parameters within the context of general relativity. ... Accelerating universe is a term for the idea that our universe is undergoing divergent rapid expansion. ... For other uses, see Big Bang (disambiguation). ...

Measurement, characterization, and interpretation

The spectrum of light that comes from a single source (see idealized spectrum illustration top-right) can be measured. To determine the redshift, features in the spectrum such as absorption lines, emission lines, or other variations in light intensity, are searched for. If found, these features can be compared with known features in the spectrum of various chemical compounds found in experiments where that compound is located on earth. A very common atomic element in space is hydrogen. The spectrum of originally featureless light shined through hydrogen will show a signature spectrum specific to hydrogen that has features at regular intervals. If restricted to absorption lines it would look similar to the illustration (top right). If the same pattern of intervals is seen in an observed spectrum from a distant source but occurring at shifted wavelengths, it can be identified as hydrogen too. If the same spectral line is identified in both spectra but at different wavelengths then the redshift can be calculated using the table below. Determining the redshift of an object in this way requires a frequency- or wavelength-range. In order to calculate the redshift one has to know the wavelength of the emitted light in the rest frame of the source, in other words, the wavelength that would be measured by an observer located adjacent to and comoving with the source. Since in astronomical applications this measurement cannot be done directly, because that would require travelling to the distant star of interest, the method using spectral lines described here is used instead. Redshifts cannot be calculated by looking at unidentified features whose rest-frame frequency is unknown, or with a spectrum that is featureless or white noise (random fluctuations in a spectrum).^[17] Visible light redirects here. ... A spectral line is a dark or bright line in an otherwise uniform and continuous spectrum, resulting from an excess or deficiency of photons in a narrow frequency range, compared with the nearby frequencies. ... A spectral line is a dark or bright line in an otherwise uniform and continuous spectrum, resulting from an excess or deficiency of photons in a narrow frequency range, compared with the nearby frequencies. ... Luminous intensity is a measure of the energy emitted by a light source in a particular direction. ... The periodic table of the chemical elements A chemical element, or element, is a type of atom that is distinguished by its atomic number; that is, by the number of protons in its nucleus. ... This article is about the chemistry of hydrogen. ... A hydrogen atom is an atom of the element hydrogen. ... Calculated spectrum of a generated approximation of white noise White noise is a random signal (or process) with a flat power spectral density. ...

Redshift (and blue shift) 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 z. If λ represents wavelength and f represents frequency (note, λf = c where c is the speed of light), then z is defined by the equations: In the physical sciences, a dimensionless number (or more precisely, a number with the dimensions of 1) is a quantity which describes a certain physical system and which is a pure number without any physical units; it does not change if one alters ones system of units of measurement... A line showing the speed of light on a scale model of Earth and the Moon, taking about 1â…“ seconds to traverse that distance. ...

Calculation of redshift, z

Based on wavelength	Based on frequency

After z is measured, the distinction between redshift and blue shift is simply a matter of whether z is positive or negative. See the mechanisms section below for some basic interpretations that follow when either a redshift or blue shift is observed. For example, Doppler effect blue shifts (z < 0) are associated with objects approaching (moving closer to) the observer with the light shifting to greater energies. Conversely, Doppler effect redshifts (z > 0) are associated with objects receding (moving away) from the observer with the light shifting to lower energies. Likewise, gravitational blue shifts are associated with light emitted from a source residing within a weaker gravitational field observed within a stronger gravitational field, while gravitational redshifting implies the opposite conditions. A source of waves moving to the left. ... A gravitational field is a model used within physics to explain how gravity exists in the universe. ... A gravitational field is a model used within physics to explain how gravity exists in the universe. ...

Mechanisms

A single photon propagated through a vacuum can redshift in several distinct ways. Each of these mechanisms produces a Doppler-like redshift, meaning that z is independent of wavelength. These mechanisms are described with Galilean, Lorentz, or general relativistic transformations between one frame of reference and another.^[2] In modern physics the photon is the elementary particle responsible for electromagnetic phenomena. ... Look up Vacuum in Wiktionary, the free dictionary. ... The Galilean transformation is used to transform between the coordinates of two reference frames which differ only by constant relative motion within the constructs of Newtonian physics. ... In physics, the Lorentz transformation converts between two different observers measurements of space and time, where one observer is in constant motion with respect to the other. ... For a generally accessible and less technical introduction to the topic, see Introduction to general relativity. ... This article or section is in need of attention from an expert on the subject. ...

Redshift Summary

Redshift type	Frame transformation law	Example of a metric[18]	Definition[19]
Doppler redshift	Galilean transformation	Euclidean metric
Relativistic Doppler	Lorentz transformation	Minkowski metric
Cosmological redshift	General relativistic tr.	FRW metric
Gravitational redshift	General relativistic tr.	Schwarzschild metric

The Galilean transformation is used to transform between the coordinates of two reference frames which differ only by constant relative motion within the constructs of Newtonian physics. ... The Euclidean distance of two points x = (x1,...,xn) and y = (y1,...,yn) in Euclidean n-space is computed as It is the ordinary distance between the two points that one would measure with a ruler, which can be proven by repeated application of the Pythagorean theorem. ... In physics, the Lorentz transformation converts between two different observers measurements of space and time, where one observer is in constant motion with respect to the other. ... In physics and mathematics, Minkowski space (or Minkowski spacetime) is the mathematical setting in which Einsteins theory of special relativity is most conveniently formulated. ... For a generally accessible and less technical introduction to the topic, see Introduction to general relativity. ... The Friedmann-Lemaître-Robertson-Walker (FLRW) metric describes a homogeneous, isotropic expanding/contracting universe. ... For a generally accessible and less technical introduction to the topic, see Introduction to general relativity. ... It has been suggested that Deriving the Schwarzschild solution be merged into this article or section. ...

Doppler effect

Main article: Doppler effect

If a source of the light is moving away from an observer, then redshift (z > 0) occurs; if the source moves towards the observer, then blue shift (z < 0) occurs. This is true for all electromagnetic waves and is explained by the Doppler effect. Consequently, this type of redshift is called the Doppler redshift. If the source moves away from the observer with velocity v, then, ignoring relativistic effects, the redshift is given by A source of waves moving to the left. ... Blue shift is the opposite of redshift, the latter being much more noted due to its importance to modern astronomy. ... A source of waves moving to the left. ... This article is about velocity in physics. ...

    (Since , see below)

where c is the speed of light. In the classical Doppler effect, the frequency of the source is not modified, but the recessional motion causes the illusion of a lower frequency. A line showing the speed of light on a scale model of Earth and the Moon, taking about 1â…“ seconds to traverse that distance. ...

Relativistic Doppler effect

Main article: Relativistic Doppler effect

A more complete treatment of the Doppler redshift requires considering relativistic effects associated with motion of sources close to the speed of light. A complete derivation of the effect can be found in the article on the relativistic Doppler effect. In brief, objects moving close to the speed of light will experience deviations from the above formula due to the time dilation of special relativity which can be corrected for by introducing the Lorentz factor γ into the classical Doppler formula as follows: A source of light waves moving to the right with velocity 0. ... A source of light waves moving to the right with velocity 0. ... Time dilation is the phenomenon whereby an observer finds that anothers clock which is physically identical to their own is ticking at a slower rate as measured by their own clock. ... For a less technical and generally accessible introduction to the topic, see Introduction to special relativity. ... It has been suggested that Lorentz term be merged into this article or section. ...

This phenomenon was first observed in a 1938 experiment performed by Herbert E. Ives and G.R. Stilwell, called the Ives-Stilwell experiment.^[20] The Ives-Stilwell experiment exploits the Transverse Doppler effect (TDE) described by Albert Einstein in his 1905 paper. ...

Since the Lorentz factor is dependent only on the magnitude of the velocity, this causes the redshift associated with the relativistic correction to be independent of the orientation of the source movement. In contrast, the classical part of the formula is dependent on the projection of the movement of the source into the line of sight which yields different results for different orientations. Consequently, for an object moving at an angle θ to the observer (zero angle is directly away from the observer), the full form for the relativistic Doppler effect becomes: The magnitude of a mathematical object is its size: a property by which it can be larger or smaller than other objects of the same kind; in technical terms, an ordering of the class of objects to which it belongs. ... The scalar resolute of two vectors, in the direction of (also on ), is given by: or (where is the angle between vectors and ). The scalar resolute is a scalar, and represents the length of the vector mapped onto vector . ... When viewing a scene, as in optics, photography, or even hunting, the line of sight is the straight line between the observer and the target. ...

and for motion solely in the line of sight (θ = 0°), this equation reduces to:

For the special case that the source is moving at right angles (θ = 90°) to the detector, the relativistic redshift is known as the transverse redshift, and a redshift: This article is about angles in geometry. ... In special relativity, the transverse Doppler effect is the nominal redshift component associated with transverse (i. ...

is measured, even though the object is not moving away from the observer. Even if the source is moving towards the observer, if there is a transverse component to the motion then there is some speed at which the dilation just cancels the expected blue shift and at higher speed the approaching source will be redshifted.^[21] In general, a things components are its parts; the things that compose it. ...

Expansion of space

Main article: Metric expansion of space

In the early part of the twentieth century, Slipher, Hubble and others made the first measurements of the redshifts and blue shifts of galaxies beyond the Milky Way. They initially interpreted these redshifts and blue shifts as due solely to the Doppler effect, but later Hubble discovered a rough correlation between the increasing redshifts and the increasing distance of galaxies. Theorists almost immediately realized that these observations could be explained by a different mechanism for producing redshifts. Hubble's law of the correlation between redshifts and distances is required by models of cosmology derived from general relativity that have a metric expansion of space.^[16] As a result, photons propagating through the expanding space are stretched, creating the cosmological redshift. This differs from the Doppler effect redshifts described above because the velocity boost (i.e. the Lorentz transformation) between the source and observer is not due to classical momentum and energy transfer, but instead the photons increase in wavelength and redshift as the space through which they are traveling expands.^[22] This effect is prescribed by the current cosmological model as an observable manifestation of the time-dependent cosmic scale factor (a) in the following way: This box:      The metric expansion of space is a key part of sciences current understanding of the universe, whereby spacetime itself is described by a metric which changes over time in such a way that the spatial dimensions grow or stretch as the universe gets older. ... For other uses, see Milky Way (disambiguation). ... This box:      Hubbles law is a statement in physical cosmology which states that the redshift in light coming from distant galaxies is proportional to their distance. ... This box:      The metric expansion of space is a key part of sciences current understanding of the universe, whereby spacetime itself is described by a metric which changes over time in such a way that the spatial dimensions grow or stretch as the universe gets older. ... Hubbles law is the statement in astronomy that the redshift in light coming from distant galaxies is proportional to their distance. ... In physics, the Lorentz transformation converts between two different observers measurements of space and time, where one observer is in constant motion with respect to the other. ... This article is about momentum in physics. ... // The Friedmann-Lemaître-Robertson-Walker (FLRW) metric is an exact solution of the Einstein field equations of general relativity and which describes a homogeneous, isotropic expanding/contracting universe. ... The scale factor, parameter of Friedmann-Lemaître-Robertson-Walker model, is a function of time which represents the relative expansion of the universe. ...

This type of redshift is called the cosmological redshift or Hubble redshift. If the universe were contracting instead of expanding, we would see distant galaxies blue shifted by an amount proportional to their distance instead of redshifted.^[23] Hubbles law is the statement in astronomy that the redshift in light coming from distant galaxies is proportional to their distance. ...

These galaxies are not receding simply by means of a physical velocity in the direction away from the observer; instead, the intervening space is stretching, which accounts for the large-scale isotropy of the effect demanded by the cosmological principle.^[24] For cosmological redshifts of z < 0.1 the effects of spacetime expansion are minimal and observed redshifts dominated by the peculiar motions of the galaxies relative to one another that cause additional Doppler redshifts and blue shifts.^[25] The difference between physical velocity and space expansion can be illustrated by the Expanding Rubber Sheet Universe, a common cosmological analogy used to describe the expansion of space. If two objects are represented by ball bearings and spacetime by a stretching rubber sheet, the Doppler effect is caused by rolling the balls across the sheet to create peculiar motion. The cosmological redshift occurs when the ball bearings are stuck to the sheet and the sheet is stretched. (Obviously, there are dimensional problems with the model, as the ball bearings should be in the sheet, and cosmological redshift produces higher velocities than Doppler does if the distance between two objects is large enough.) The Cosmological Principle is a principle invoked in cosmology that severely restricts the large variety of possible cosmological theories: On large scales, the Universe is homogeneous and isotropic. ... For other uses of this term, see Spacetime (disambiguation). ... This box:      The metric expansion of space is a key part of sciences current understanding of the universe, whereby spacetime itself is described by a metric which changes over time in such a way that the spatial dimensions grow or stretch as the universe gets older. ...

In spite of the distinction between redshifts caused by the velocity of objects and the redshifts associated with the expanding universe, astronomers sometimes refer to "recession velocity" in the context of the redshifting of distant galaxies from the expansion of the Universe, even though it is only an apparent recession.^[26] As a consequence, popular literature often uses the expression "Doppler redshift" instead of "cosmological redshift" to describe the motion of galaxies dominated by the expansion of spacetime, despite the fact that a "cosmological recessional speed" when calculated will not equal the velocity in the relativistic Doppler equation.^[27] In particular, Doppler redshift is bound by special relativity; thus v > c is impossible while, in contrast, v > c is possible for cosmological redshift because the space which separates the objects (e.g., a quasar from the Earth) can expand faster than the speed of light.^[28] More mathematically, the viewpoint that "distant galaxies are receding" and the viewpoint that "the space between galaxies is expanding" are related by changing coordinate systems. Expressing this precisely requires working with the mathematics of the Friedmann-Robertson-Walker metric.^[29] For a less technical and generally accessible introduction to the topic, see Introduction to special relativity. ... In mathematics as applied to geometry, physics or engineering, a coordinate system is a system for assigning a tuple of numbers to each point in an n-dimensional space. ... // The Friedmann-Lemaître-Robertson-Walker (FLRW) metric is an exact solution of the Einstein field equations of general relativity and which describes a homogeneous, isotropic expanding/contracting universe. ...

Gravitational redshift

Main article: Gravitational redshift

A graphical representation of the gravitational redshift due to a neutron star

In the theory of general relativity, there is time dilation within a gravitational well. This is known as the gravitational redshift or Einstein Shift.^[30] The theoretical derivation of this effect follows from the Schwarzschild solution of the Einstein equations which yields the following formula for redshift associated with a photon traveling in the gravitational field of an uncharged, nonrotating, spherically symmetric mass: Graphic representing the gravitational redshift of a neutron star (not exact) In physics, light or other forms of electromagnetic radiation of a certain wavelength originating from a source placed in a region of stronger gravitational field (and which could be said to have climbed uphill out of a gravity well... Image File history File links Gravitational_redshift_neutron_star. ... Image File history File links Gravitational_redshift_neutron_star. ... Graphic representing the gravitational redshift of a neutron star (not exact) In physics, light or other forms of electromagnetic radiation of a certain wavelength originating from a source placed in a region of stronger gravitational field (and which could be said to have climbed uphill out of a gravity well... For the story by Larry Niven, see Neutron Star (story). ... For a generally accessible and less technical introduction to the topic, see Introduction to general relativity. ... Graphic representing the gravitational redshift of a neutron star (not exact) In physics, light or other forms of electromagnetic radiation of a certain wavelength originating from a source placed in a region of stronger gravitational field (and which could be said to have climbed uphill out of a gravity well... Introduction In Einsteins theory of general relativity, the Schwarzschild metric is the most general static, spherically symmetric solution of the vacuum field equations. ... The Einstein field equations (EFE) or Einsteins equations are a set of ten equations in Einsteins theory of general relativity in which the fundamental force of gravitation is described as a curved spacetime caused by matter and energy. ... A gravitational field is a model used within physics to explain how gravity exists in the universe. ... Electric charge is a fundamental property of some subatomic particles, which determines their electromagnetic interactions. ... This article is about rotation as a movement of a physical body. ... In mechanics and geometry, the rotation group is the set of all rotations of 3-dimensional Euclidean space, R3. ...

where

• is the gravitational constant,
• is the mass of the object creating the gravitational field,
• is the radial coordinate of the observer (which is analogous to the classical distance from the center of the object, but is actually a Schwarzschild coordinate), and
• is the speed of light.

This gravitational redshift result can be derived from the assumptions of special relativity and the equivalence principle; the full theory of general relativity is not required.^[31] The gravitational constant G is a key element in Newtons law of universal gravitation. ... For other uses, see Mass (disambiguation). ... In General Relativity, Schwarzschild coordinates refers to the coordinate system of the Schwarzschild metric. ... A line showing the speed of light on a scale model of Earth and the Moon, taking about 1â…“ seconds to traverse that distance. ... For a less technical and generally accessible introduction to the topic, see Introduction to special relativity. ... In the physics of relativity, the equivalence principle is applied to several related concepts dealing with gravitation and the uniformity of physical measurements in different frames of reference. ...

The effect is very small but measurable on Earth using the Mossbauer effect and was first observed in the Pound-Rebka experiment.^[32] However, it is significant near a black hole, and as an object approaches the event horizon the red shift becomes infinite. It is also the dominant cause of large angular-scale temperature fluctuations in the cosmic microwave background radiation (see Sachs-Wolfe effect).^[33] The Mössbauer effect, a physical phenomenon discovered by Rudolf Mössbauer in 1957, refers to the resonant and recoil-free emission and absorption of gamma rays by atoms bound in a solid form. ... The Pound-Rebka experiment is a well known experiment in general relativity. ... For other uses, see Black hole (disambiguation). ... For the science fiction film, see Event Horizon (film). ... CMB redirects here. ... The Sachs-Wolfe effect is a property of the cosmic background radiation (CBR), in which gravitational bodies redshift the CBR, causing it to appear uneven. ...

Observations in astronomy

The redshift observed in astronomy can be measured because the emission and absorption spectra for atoms are distinctive and well known, calibrated from spectroscopic experiments in laboratories on Earth. When the redshift of various absorption and emission lines from a single astronomical object is measured, z is found to be remarkably constant. Although distant objects may be slightly blurred and lines broadened, it is by no more than can be explained by thermal or mechanical motion of the source. For these reasons and others, the consensus among astronomers is that the redshifts they observe are due to some combination of the three established forms of Doppler-like redshifts. Alternative hypotheses are not generally considered plausible.^[34] An elements emission spectrum is the relative intensity of electromagnetic radiation of each frequency it emits when it is heated (or more generally when it is excited). ... A materials absorption spectrum shows the fraction of incident electromagnetic radiation absorbed by the material over a range of frequencies. ... For other uses, see Atom (disambiguation). ... Animation of the dispersion of light as it travels through a triangular prism. ... This article does not cite any references or sources. ... thermal is related to heat, and motion means moving. ... This article or section is in need of attention from an expert on the subject. ...

Spectroscopy, as a measurement, is considerably more difficult than simple photometry, which measures the brightness of astronomical objects through certain filters.^[35] When photometric data is all that is available (for example, the Hubble Deep Field and the Hubble Ultra Deep Field), astronomers rely on a technique for measuring photometric redshifts.^[36] Due to the filter being sensitive to a range of wavelengths and the technique relying on making many assumptions about the nature of the spectrum at the light-source, errors for these sorts of measurements can range up to δz = 0.5, and are much less reliable than spectroscopic determinations.^[37] However, photometry does allow at least for a qualitative characterization of a redshift. For example, if a sun-like spectrum had a redshift of z = 1, 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 two (1+z) (see K correction for more details on the photometric consequences of redshift).^[38] Photometry is a technique of astronomy concerned with measuring the flux, or intensity of an astronomical objects electromagnetic radiation. ... Brightness is an attribute of visual perception in which a source appears to emit a given amount of light. ... Coloured and Neutral Density filters An optical filter is a device which selectively transmits light having certain properties (often, a particular range of wavelengths, that is, range of colours of light), while blocking the remainder. ... The Hubble Deep Field The Hubble Deep Field (HDF) is the result of a series of observations by the Hubble Space Telescope of a small region of the northern celestial hemisphere. ... This high-resolution image of the HUDF includes galaxies of various ages, sizes, shapes, and colors. ... A photometric redshift is an estimate for the distance of an astronomical object, such as a galaxy or quasar. ... Observational error is the difference between a measured value of quantity and its true value. ... For other uses, see Infrared (disambiguation). ... As the temperature decreases, the peak of the black body radiation curve moves to lower intensities and longer wavelengths. ... K correction is a type of calculation that can be performed on redshifts that allow a measurement taken at a redshift z to be converted to a measurement at redshift zero. ...

Local observations

A picture of the solar corona taken with the LASCO C1 coronagraph. The picture is a color coded image of the doppler shift of the FeXIV 5308 Å line, caused by the coronal plasma velocity towards or away from the satellite.

In nearby objects (within our Milky Way galaxy) observed redshifts are almost always related to the line of sight velocities associated with the objects being observed. Observations of such redshifts and blue shifts have enabled astronomers to measure velocities and parametrize the masses of the orbiting stars in spectroscopic binaries, a method first employed in 1868 by British astronomer William Huggins.^[8] Similarly, small redshifts and blue shifts detected in the spectroscopic measurements of individual stars are one way astronomers have been able to diagnose and measure the presence and characteristics of planetary systems around other stars.^[39] Measurements of redshifts to fine detail are used in helioseismology to determine the precise movements of the photosphere of the Sun.^[40] Redshifts have also been used to make the first measurements of the rotation rates of planets,^[41] velocities of interstellar clouds,^[42] the rotation of galaxies,^[2] and the dynamics of accretion onto neutron stars and black holes which exhibit both Doppler and gravitational redshifts.^[43] Additionally, the temperatures of various emitting and absorbing objects can be obtained by measuring Doppler broadening — effectively redshifts and blue shifts over a single emission or absorption line.^[44] By measuring the broadening and shifts of the 21-centimeter hydrogen line in different directions, astronomers have been able to measure the recessional velocities of interstellar gas, which in turn reveals the rotation curve of our Milky Way.^[2] Similar measurements have been performed on other galaxies, such as Andromeda.^[2] As a diagnostic tool, redshift measurements are one of the most important spectroscopic measurements made in astronomy. Image File history File links No higher resolution available. ... Image File history File links No higher resolution available. ... The Solar and Heliospheric Observatory (SOHO) is a spacecraft that was launched on an Atlas IIAS launch vehicle on 2 December 1995 to study the Sun, and began normal operations in May 1996. ... For other uses, see Milky Way (disambiguation). ... When viewing a scene, as in optics, photography, or even hunting, the line of sight is the straight line between the observer and the target. ... This article is about velocity in physics. ... For other uses, see Mass (disambiguation). ... Two bodies with a slight difference in mass orbiting around a common barycenter. ... This article is about the astronomical object. ... For the band of the same name, see: Binary Star (band) Hubble image of the Sirius binary system, in which Sirius B can be clearly distinguished (lower left). ... William Huggins Sir William Huggins, OM , FRS (February 7, 1824 – May 12, 1910) was a British astronomer. ... Any planet is an extremely faint light source compared to its parent star. ... An extrasolar planet, or exoplanet, is a planet beyond the Solar System. ... A computer generated image showing the pattern of a p-mode solar acoustic oscillation both in the interior and on the surface of the sun. ... Solar disk redirects here. ... Sol redirects here. ... This article is about rotation as a movement of a physical body. ... This article is about the astronomical term. ... Interstellar cloud is the generic name given to an accumulation of gas, plasma and dust in our and other galaxies. ... The galaxy rotation problem is the discrepancy between the observed rotation speeds of matter in the disk portions of spiral galaxies and the predictions of Newtonian dynamics considering the luminous mass. ... In physics, dynamics is the branch of classical mechanics that is concerned with the effects of forces on the motion of objects. ... The accretion theory, in astrophysics, is a scientific theory of the formation of our Solar system. ... For the story by Larry Niven, see Neutron Star (story). ... For other uses, see Black hole (disambiguation). ... For other uses, see Temperature (disambiguation). ... Doppler broadening is a broadening of spectral lines due to thermal agitation. ... This article or section does not adequately cite its references or sources. ... Recessional Velocity is a term used to describe the rate at which an object is moving away, typically from Earth. ... The interstellar medium (or ISM) is a term used in astronomy to describe the rarefied gas and dust that exists between the stars (or their immediate circumstellar environment) within a galaxy. ... The rotation curve of a galaxy; that is, the orbital velocity as a function of distance from the centre of the galaxy. ... The Andromeda Galaxy (also known as M31 or NGC 224; older texts often call it the Andromeda Nebula) is a giant spiral galaxy in the Local Group, together with the Milky Way galaxy. ... High resolution spectrum of the Sun showing thousands of elemental absorption lines (fraunhofer lines). ...

Extragalactic observations

Physical cosmology

Universe · Big Bang Age of the universe Timeline of the Big Bang Ultimate fate of the universe Early Universe Inflation · Nucleosynthesis GWB · Neutrino Background Cosmic microwave background Expanding universe Redshift · Hubble's law Metric expansion of space Friedmann equations FLRW metric Structure formation Shape of the universe Structure formation Galaxy formation Large-scale structure Components Lambda-CDM model Dark energy · Dark matter History Timeline of cosmology... Experiments Observational cosmology 2dF · SDSS COBE · BOOMERanG · WMAP Scientists Einstein · Hawking · Friedman · Lemaître · Hubble · Penzias · Wilson · Gamow · Dicke · Zel'dovich · Mather · Rubin · Smoot· others

This box: view • talk • edit

The most distant objects exhibit larger redshifts corresponding to the Hubble flow of the universe. The largest observed redshift, corresponding to the greatest distance and furthest back in time, is that of the cosmic microwave background radiation; the numerical value of its redshift is about z = 1089 (z = 0 corresponds to present time), and it shows the state of the Universe about 13.7 billion years ago, and 379,000 years after the initial moments of the Big Bang.^[45] This article is about the physics subject. ... For other uses, see Universe (disambiguation). ... For other uses, see Big Bang (disambiguation). ... This box:      This article is about scientific estimates of the age of the universe. ... This box:      A graphical timeline is available here: Graphical timeline of the Big Bang This timeline of the Big Bang describes the events according to the scientific theory of the Big Bang, using the cosmological time parameter of comoving coordinates. ... This box:      The ultimate fate of the universe is a topic in physical cosmology. ... In cosmology, Big Bang nucleosynthesis (or primordial nucleosynthesis) refers to the production of nuclei other than H-1, the normal, light hydrogen, during the early phases of the universe, shortly after the Big Bang. ... This article or section is in need of attention from an expert on the subject. ... The Cosmic Neutrino Background (CNB) is the background particle radiation composed of neutrinos. ... CMB redirects here. ... This box:      Hubbles law is a statement in physical cosmology which states that the redshift in light coming from distant galaxies is proportional to their distance. ... This box:      The metric expansion of space is a key part of sciences current understanding of the universe, whereby spacetime itself is described by a metric which changes over time in such a way that the spatial dimensions grow or stretch as the universe gets older. ... The Friedmann equations relate various cosmological parameters within the context of general relativity. ... // The Friedmann-Lemaître-Robertson-Walker (FLRW) metric is an exact solution of the Einstein field equations of general relativity and which describes a homogeneous, isotropic expanding/contracting universe. ... The shape of the Universe is an informal name for a subject of investigation within physical cosmology. ... It has been suggested that this article or section be merged into Large-scale structure of the cosmos. ... In astrophysics, the questions of galaxy formation and evolution are: How, from a homogeneous universe, did we obtain the very heterogeneous one we live in? How did galaxies form? How do galaxies change over time? A spectacular head-on collision between two galaxies is seen in this NASA Hubble Space... Astronomy and cosmology examine the universe to understand the large-scale structure of the cosmos. ... A pie chart indicating the proportional composition of different energy-density components of the universe. ... In physical cosmology, dark energy is a hypothetical form of energy that permeates all of space and tends to increase the rate of expansion of the universe. ... For other uses, see Dark matter (disambiguation). ... This lists a timeline of cosmological theories and discoveries. ... Observational cosmology is the study of the structure, the evolution and the origin of the universe through observation, using instruments such as telescopes and cosmic ray detectors. ... In astronomy, the 2dF Galaxy Redshift Survey (Two-degree-Field Galaxy Redshift Gurvey), or 2dFGRS is a redshift survey conducted by the Anglo-Australian Observatory in the 1990s. ... SDSS Logo The Sloan Digital Sky Survey or SDSS is a major multi-filter imaging and spectroscopic redshift survey using a dedicated 2. ... The Cosmic Background Explorer (COBE), also referred to as Explorer 66, was the first satellite built dedicated to cosmology. ... The Telescope being readied for launch The BOOMERanG experiment (Balloon Observations Of Millimetric Extragalactic Radiation and Geophysics) measured the cosmic microwave background radiation of a part of the sky during three sub-orbital (high altitude) balloon flights. ... Artist depiction of the WMAP satellite at the L2 point The Wilkinson Microwave Anisotropy Probe (WMAP) is a NASA satellite whose mission is to survey the sky to measure the temperature of the radiant heat left over from the Big Bang. ... “Einstein” redirects here. ... Stephen William Hawking, CH, CBE, FRS, FRSA, (born 8 January 1942) is a British theoretical physicist. ... Alexander Alexandrovich Friedman or Friedmann (Александр Александрович Фридман) (June 16, 1888 – September 16, 1925) was a Russian cosmologist and mathematician. ... Monsignor Georges Lemaître, priest and scientist. ... Edwin Powell Hubble (November 20, 1889 – September 28, 1953) was an American astronomer. ... Arno Allan Penzias (born April 26, 1933) is an American physicist and winner of the 1978 Nobel Prize in physics. ... Robert Woodrow Wilson Robert Woodrow Wilson (born January 10, 1936) is an American physicist. ... George Gamow (pronounced GAM-off) (March 4, 1904 – August 19, 1968) , born Georgiy Antonovich Gamov (Георгий Антонович Гамов) was a Ukrainian born physicist and cosmologist. ... Robert Henry Dicke (May 6, 1916 – March 4, 1997) was an American experimental physicist, who made important contributions to the fields of astrophysics, atomic physics, cosmology and gravity. ... Yakov Borisovich Zeldovich (Russian:Яков Борисович Зельдович) (March 8, 1914 – December 2, 1987) was a prolific Soviet physicist. ... John Cromwell Mather (b. ... Vera (Cooper) Rubin (born 23 July 1928) is an astronomer who has done pioneering work on galaxy rotation rates. ... George Fitzgerald Smoot III (born February 20, 1945) is an American astrophysicist and cosmologist awarded the 2006 Nobel Prize in Physics with John C. Mather for their discovery of the black body form and anisotropy of the cosmic microwave background radiation. This work helped cement the big-bang theory of... This is a list of cosmologists. ... This box:      Hubbles law is a statement in physical cosmology which states that the redshift in light coming from distant galaxies is proportional to their distance. ... CMB redirects here. ... For other uses, see Universe (disambiguation). ... For other uses, see Big Bang (disambiguation). ...

The luminous point-like cores of quasars were the first "high-redshift" (z > 0.1) objects discovered before the improvement of telescopes allowed for the discovery of other high-redshift galaxies. This article is about the astronomical object. ...

For galaxies more distant than the Local Group and the nearby Virgo Cluster, but within a thousand megaparsecs or so, the redshift is approximately proportional to the galaxy's distance. This correlation was first observed by Edwin Hubble and has come to be known as Hubble's law. Vesto Slipher was the first to discover galactic redshifts, in about the year 1912, while Hubble correlated Slipher's measurements with distances he measured by other means to formulate his Law. In the widely accepted cosmological model based on general relativity, redshift is mainly a result of the expansion of space: this means that the farther away a galaxy is from us, the more the space has expanded in the time since the light left that galaxy, so the more the light has been stretched, the more redshifted the light is, and so the faster it appears to be moving away from us. Hubble's law follows in part from the Copernican principle.^[46] Because it is usually not known how luminous objects are, measuring the redshift is easier than more direct distance measurements, so redshift is sometimes in practice converted to a crude distance measurement using Hubble's law. A member of the Local Group of galaxies, irregular galaxy Sextans A is 4. ... A sky field near some of the brighter galaxies in the Virgo cluster. ... A parsec is the distance from the Earth to an astronomical object which has a parallax angle of one arcsecond. ... Edwin Powell Hubble (November 20, 1889 – September 28, 1953) was an American astronomer. ... This box:      Hubbles law is a statement in physical cosmology which states that the redshift in light coming from distant galaxies is proportional to their distance. ... Vesto Melvin Slipher (November 11, 1875 – November 8, 1969) was an American astronomer. ... The cosmic distance ladder is the succession of methods by which astronomers determine the distances to celestial objects. ... For a generally accessible and less technical introduction to the topic, see Introduction to general relativity. ... This box:      Hubbles law is a statement in physical cosmology which states that the redshift in light coming from distant galaxies is proportional to their distance. ... In cosmology, the Copernican principle, named after Nicolaus Copernicus, states [1] More recently, the principle is generalised to the relativistic concept that humans are not privileged observers of the universe. ... This article does not cite any references or sources. ...

Gravitational interactions of galaxies with each other and clusters cause a significant scatter in the normal plot of the Hubble diagram. The peculiar velocities associated with galaxies superimpose a rough trace of the mass of virialized objects in the universe. This effect leads to such phenomena as nearby galaxies (such as the Andromeda Galaxy) exhibiting blue shifts as we fall towards a common barycenter, and redshift maps of clusters showing a Finger of God effect due to the scatter of peculiar velocities in a roughly spherical distribution.^[47] This added component gives cosmologists a chance to measure the masses of objects independent of the mass to light ratio (the ratio of a galaxy's mass in solar masses to its brightness in solar luminosities), an important tool for measuring dark matter.^[48] Gravity redirects here. ... This article is about mathematics. ... The term peculiar velocity refers to the components of a receding galaxys velocity that cannot be explained by Hubbles law. ... For other uses, see Mass (disambiguation). ... In mechanics, the virial theorem provides a general equation relating the average total kinetic energy of a system with its average total potential energy , where angle brackets represent the average of the enclosed quantity. ... The Andromeda Galaxy (IPA: , also known as Messier 31, M31, or NGC 224; often referred to as the Great Andromeda Nebula in older texts) is a spiral galaxy approximately 2. ... In physics, the center of mass of a system of particles is a specific point at which, for many purposes, the systems mass behaves as if it was concentrated. ... Fingers of God in a portion of the Sloan Digital Sky Survey; image from the Cosmus Open Source Science Outreach project [1]. Fingers of God is an effect in cosmology that causes clusters of galaxies to be elongated in redshift space, with an axis of elongation pointed toward the observer... In physical cosmology the mass to light ratio is a comparison of the total mass of a galaxy or a cluster compared to its luminosity. ... For other uses, see Dark matter (disambiguation). ...

The Hubble law's linear relationship between distance and redshift assumes that the rate of expansion of the universe is constant. However, when the universe was much younger, the expansion rate, and thus the Hubble "constant", was larger than it is today. For more distant galaxies, then, whose light has been travelling to us for much longer times, the approximation of constant expansion rate fails, and the Hubble law becomes a non-linear integral relationship and dependent on the history of the expansion rate since the emission of the light from the galaxy in question. Observations of the redshift-distance relationship can be used, then, to determine the expansion history of the universe and thus the matter and energy content.

While it was long believed that the expansion rate has been continuously decreasing since the Big Bang, recent observations of the redshift-distance relationship using Type Ia supernovae have suggested that in comparatively recent times the expansion rate of the universe has begun to accelerate. Multiwavelength X-ray image of the remnant of Keplers Supernova, SN 1604. ... The accelerating universe is the observation that the universe appears to be expanding at an accelerated rate. ...

Highest redshifts

Currently, the highest measured quasar redshift is z = 6.4,^[49] with the highest confirmed spectroscopic redshift of a galaxy being that of IOK-1^[50], at a redshift z = 6.96, and the highest lensed galaxy redshift being z = 7.0^[51] while as-yet unconfirmed reports from a gravitational lens observed in a distant galaxy cluster may indicate a galaxy with a redshift of z = 10.^[52] IOK-1, probably the oldest galaxy yet found, was discovered in September 2006 by Masanori Iye at National Astronomical Observatory of Japan using the Subaru Telescope in Hawaii. ... This article or section is in need of attention from an expert on the subject. ... The galaxies of HCG 87, about four hundred million light-years distant. ...

The highest known redshift radio galaxy (TN J0924-2201) is at a redshift z = 5.2 ^[53] and the highest known redshift molecular material is the detection of emission from the CO molecule from the quasar SDSS J1148+5251 at z = 6.42 ^[54]

Redshift surveys

Main article: Redshift survey

Rendering of the 2dFGRS data

With the advent of automated telescopes and improvements in spectroscopes, a number of collaborations have been made to map the universe in redshift space. By combining redshift with angular position data, a redshift survey maps the 3D distribution of matter within a field of the sky. These observations are used to measure properties of the large-scale structure of the universe. The Great Wall, a vast supercluster of galaxies over 500 million light-years wide, provides a dramatic example of a large-scale structure that redshift surveys can detect.^[55] In astronomy, a redshift survey is a survey of a section of the sky to measure the redshift of astronomical objects. ... Image File history File links Download high resolution version (900x529, 124 KB) // Description en:2dF Galaxy Redshift Survey data. ... Image File history File links Download high resolution version (900x529, 124 KB) // Description en:2dF Galaxy Redshift Survey data. ... This article does not cite any references or sources. ... High resolution spectrum of the Sun showing thousands of elemental absorption lines (fraunhofer lines). ... Astronomy and cosmology examine the universe to understand the large-scale structure of the cosmos. ... The Great Wall, sometimes more specifically referred to as the CfA2 Great Wall, is the second largest known super-structure in the Universe (the largest being Sloan Great Wall). ... Superclusters are large groupings of smaller galaxy groups and clusters, and are among the largest structures of the cosmos. ... A light-year, symbol ly, is the distance light travels in one year: exactly 9. ...

The first redshift survey was the CfA Redshift Survey, started in 1977 with the initial data collection completed in 1982.^[56] More recently, the 2dF Galaxy Redshift Survey determined the large-scale structure of one section of the Universe, measuring z-values for over 220,000 galaxies; data collection was completed in 2002, and the final data set was released 30 June 2003.^[57] (In addition to mapping large-scale patterns of galaxies, 2dF established an upper limit on neutrino mass.) Another notable investigation, the Sloan Digital Sky Survey (SDSS), is ongoing as of 2005 and aims to obtain measurements on around 100 million objects.^[58] SDSS has recorded redshifts for galaxies as high as 0.4, and has been involved in the detection of quasars beyond z = 6. The DEEP2 Redshift Survey uses the Keck telescopes with the new "DEIMOS" spectrograph; a follow-up to the pilot program DEEP1, DEEP2 is designed to measure faint galaxies with redshifts 0.7 and above, and it is therefore planned to provide a complement to SDSS and 2dF.^[59] The Center for Astrophysics (CfA) Redshift Survey was the first attempt to map the large-scale structure of the universe. ... In astronomy, the 2dF Galaxy Redshift Survey (Two-degree-Field Galaxy Redshift Gurvey), or 2dFGRS is a redshift survey conducted by the Anglo-Australian Observatory in the 1990s. ... A data set (or dataset) is a collection of data, usually presented in tabular form. ... is the 181st day of the year (182nd in leap years) in the Gregorian calendar. ... Year 2003 (MMIII) was a common year starting on Wednesday of the Gregorian calendar. ... For other uses, see Neutrino (disambiguation). ... SDSS Logo The Sloan Digital Sky Survey or SDSS is a major multi-filter imaging and spectroscopic redshift survey using a dedicated 2. ... This article is about the astronomical object. ... The DEEP2 Survey or DEEP2 is a Redshift survey of the Redshift~1 universe. ... The W. M. Keck Observatory is home to the two largest optical/near-infrared telescopes at the 4,145 meter (13,600 ft) summit of Mauna Kea in Hawaii. ... For Acoustic uses in spectrographs of sound waves, see below. ...

Effects due to physical optics or radiative transfer

The interactions and phenomena summarized in the subjects of radiative transfer and physical optics can result in shifts in the wavelength and frequency of electromagnetic radiation. In such cases the shifts correspond to a physical energy transfer to matter or other photons rather than being due to a transformation between reference frames. These shifts can be due to such physical phenomena as coherence effects or the scattering of electromagnetic radiation whether from charged elementary particles, from particulates, or from fluctuations of the index of refraction in a dielectric medium as occurs in the radio phenomenon of radio whistlers.^[2] While such phenomena are sometimes referred to as "redshifts" and "blue shifts", the physical interactions of the electromagnetic radiation field with itself or intervening matter distinguishes these phenomena from the reference-frame effects. In astrophysics, light-matter interactions that result in energy shifts in the radiation field are generally referred to as "reddening" rather than "redshifting" which, as a term, is normally reserved for the effects discussed above.^[2] The equation of radiative transfer describes the propagation of electromagnetic radiation through an atmosphere which is itself emitting radiation, absorbing radiation and scattering radiation. ... Physical Optics is the name of a high frequency approximation (short wavelength approximation) used in the electromagnetism of optics and radio. ... In optics, two non-Lambertian sources that emit beamed energy can interact in a way that causes a shift in the spectral lines. ... Scattering is a general physical process whereby some forms of radiation, such as light, sound or moving particles, for example, are forced to deviate from a straight trajectory by one or more localized non-uniformities in the medium through which it passes. ... This box:      Electromagnetic (EM) radiation is a self-propagating wave in space with electric and magnetic components. ... This box:      Electric charge is a fundamental conserved property of some subatomic particles, which determines their electromagnetic interaction. ... For the novel, see The Elementary Particles. ... The refractive index of a material is the factor by which electromagnetic radiation is slowed down (relative to vacuum) when it travels inside the material. ... A dielectric, or electrical insulator, is a substance that is highly resistant to the flow of electric current and has a relative permittivity greater than unity. ... A Whistler is a very low frequency radio wave generated by lightning. ...

In many circumstances scattering causes radiation to redden because entropy results in the predominance of many low-energy photons over few high-energy ones (while conserving total energy).^[2] Except possibly under carefully controlled conditions, scattering does not produce the same relative change in wavelength across the whole spectrum; that is, any calculated z is generally a function of wavelength. Furthermore, scattering from random media generally occurs at many angles, and z is a function of the scattering angle. If multiple scattering occurs, or the scattering particles have relative motion, then there is generally distortion of spectral lines as well.^[2] For other uses, see: information entropy (in information theory) and entropy (disambiguation). ... This article is about the law of conservation of energy in physics. ... This article is about functions in mathematics. ... Random redirects here. ... This article is about angles in geometry. ... A spectral line is a dark or bright line in an otherwise uniform and continuous spectrum, resulting from an excess or deficiency of photons in a narrow frequency range, compared with the nearby frequencies. ...

In interstellar astronomy, visible spectra can appear redder due to scattering processes in a phenomenon referred to as interstellar reddening^[2] — similarly Rayleigh scattering causes the atmospheric reddening of the Sun seen in the sunrise or sunset and causes the rest of the sky to have a blue color. This phenomenon is distinct from redshifting because the spectroscopic lines are not shifted to other wavelengths in reddened objects and there is an additional dimming and distortion associated with the phenomenon due to photons being scattered in and out of the line of sight. The interstellar medium (or ISM) is the name astronomers give to the tenuous gas and dust that pervade interstellar space. ... Visible light redirects here. ... For other uses, see Red (disambiguation). ... In astronomy, interstellar reddening is a phenomenon associated with interstellar extinction where the spectrum of electromagnetic radiation from a radiation source changes characteristics from that which was emitted. ... Rayleigh scattering causing the blue hue of the sky and the reddening at sunset Rayleigh scattering (named after Lord Rayleigh) is the scattering of light, or other electromagnetic radiation, by particles much smaller than the wavelength of the light. ... Air redirects here. ... Sol redirects here. ... A typical sunrise, in New Zealand A sunrise through clouds over Oakland, California. ... A composite image showing the terminator dividing night from day, running across Europe and Africa. ... For other uses, see Sky (disambiguation). ... This article is about the colour. ... In physics, atomic spectral lines are of two types: An emission line is formed when an electron makes a transition from a particular discrete energy level of an atom, to a lower energy state, emitting a photon of a particular energy and wavelength. ... Extinction is a term used in astronomy to describe the absorption of light from astronomical objects by matter between them and the observer. ... When viewing a scene, as in optics, photography, or even hunting, the line of sight is the straight line between the observer and the target. ...

For a list of scattering processes, see Scattering. Scattering is a general physical process whereby some forms of radiation, such as light, sound or moving particles, for example, are forced to deviate from a straight trajectory by one or more localized non-uniformities in the medium through which it passes. ...

References

Notes

A magnet levitating above a high-temperature superconductor demonstrates the Meissner effect. ... This article is about the physics subject. ... The MacTutor history of mathematics archive is a website hosted by University of St Andrews in Scotland. ... The celestial sphere is divided by the celestial equator. ... One of Sir Arthur Stanley Eddingtons papers announced Einsteins theory of general relativity to the English-speaking world. ... For other uses, see NASA (disambiguation). ... The Swift Gamma-Ray Burst Mission consists of a robotic spacecraft called Swift, which was launched into orbit on November 20, 2004, at 17:16:00 UTC (12:16 PM, EST) by a Delta II 7320-10C expendable launch vehicle. ... A space observatory is any object in outer space which is used for observation of distant planets, galaxies, and other outer space objects. ... In astronomy, gamma-ray bursts (GRBs) are flashes of gamma rays that last from seconds to hours, the longer ones being followed by several days of X-ray afterglow. ... Graphic representing the gravitational redshift of a neutron star (not exact) In physics, light or other forms of electromagnetic radiation of a certain wavelength originating from a source placed in a region of stronger gravitational field (and which could be said to have climbed uphill out of a gravity well... This article is about velocity in physics. ... A line showing the speed of light on a scale model of Earth and the Moon, taking about 1â…“ seconds to traverse that distance. ... It has been suggested that Lorentz term be merged into this article or section. ... The scale factor, parameter of Friedmann-Lemaître-Robertson-Walker model, is a function of time which represents the relative expansion of the universe. ... The gravitational constant G is a key element in Newtons law of universal gravitation. ... For other uses, see Mass (disambiguation). ... In General Relativity, Schwarzschild coordinates refers to the coordinate system of the Schwarzschild metric. ... The term peculiar velocity refers to the components of a receding galaxys velocity that cannot be explained by Hubbles law. ... The American Journal of Physics is a peer-reviewed scientific journal published by the American Association of Physics Teachers devoted to the educational and cultural aspects of physics. ... A parsec is the distance from the Earth to an astronomical object which has a parallax angle of one arcsecond. ... The Hubble Space Telescope (HST; also known colloquially as the Hubble or just Hubble) is a space telescope that was carried into Earth orbit by the Space Shuttle in April 1990. ... Astronomy and Astrophysics (often referred to as A&A) is a European Journal, publishing papers on theoretical, observational and instrumental astronomy and astrophysics. ... The center of the UMass Amherst campus. ... The Astrophysical Journal is one of the foremost research journals devoted to recent developments, discoveries, and theories in astronomy and astrophysics. ... This box:      The metric expansion of space is a key part of sciences current understanding of the universe, whereby spacetime itself is described by a metric which changes over time in such a way that the spatial dimensions grow or stretch as the universe gets older. ... For other uses of this term, see Spacetime (disambiguation). ... In mathematics a metric or distance function is a function which defines a distance between elements of a set. ... For a generally accessible and less technical introduction to the topic, see Introduction to general relativity. ... In physics and mathematics, Minkowski space (or Minkowski spacetime) is the mathematical setting in which Einsteins theory of special relativity is most conveniently formulated. ... This article is about matter in physics and chemistry. ... FAQ is an abbreviation for Frequently Asked Question(s). The term refers to listed questions and answers, all supposed to be frequently asked in some context, and pertaining to a particular topic. ... John Carlos Baez (b. ... “Einstein” redirects here. ... Arthur M. Wolfe is an astrophysicist, professor and the Director of the Center for Astrophysics & Space Sciences at the University of California, San Diego. ... Fritz Zwicky (February 14, 1898 – February 8, 1974) was an American-based Swiss astronomer. ... Tired light is a class of hypothetical redshift mechanisms that were proposed as an alternative explanation for the redshift-distance relationship. ... Seeing Red. ... A non-standard cosmology is a cosmological framework that contradicts the standard model of physical cosmology. ... Geoffrey Ronald Burbidge (born September 24, 1925) is a British-American physics professor in the University of California, San Diego. ... Halton Arp in London, Oct 2000 Halton Christian Arp is an American astronomer. ... This article is about the astronomical object. ... Astronomy and Astrophysics (often referred to as A&A) is a European Journal, publishing papers on theoretical, observational and instrumental astronomy and astrophysics. ... SDSS Logo The Sloan Digital Sky Survey or SDSS is a major multi-filter imaging and spectroscopic redshift survey using a dedicated 2. ... The Astrophysical Journal is a scientific journal covering astronomy and astrophysics. ... Hermann Carl Vogel (April 3, 1841 – August 13, 1907) was a German astronomer. ... For other uses, see Venus (disambiguation). ... Vesto Melvin Slipher (November 11, 1875 – November 8, 1969) was an American astronomer. ... Oort at Leiden University Jan Hendrik Oort (April 28, 1900, Franeker – November 5, 1992, Leiden) was an internationally famous Dutch astronomer. ... Astronomy and Astrophysics (often referred to as A&A) is a European Journal, publishing papers on theoretical, observational and instrumental astronomy and astrophysics. ... The Cosmic Background Explorer (COBE), also referred to as Explorer 66, was the first satellite built dedicated to cosmology. ... Artist depiction of the WMAP satellite at the L2 point The Wilkinson Microwave Anisotropy Probe (WMAP) is a NASA satellite whose mission is to survey the sky to measure the temperature of the radiant heat left over from the Big Bang. ... The Astronomical Journal is a monthly scientific journal published by the University of Chicago Press on behalf of the American Astronomical Society. ... A digital object identifier (or DOI) is a standard for persistently identifying a piece of intellectual property on a digital network and associating it with related data, the metadata, in a structured extensible way. ... The Astrophysical Journal is one of the foremost research journals devoted to recent developments, discoveries, and theories in astronomy and astrophysics. ... Astronomy and Astrophysics (often referred to as A&A) is a European Journal, publishing papers on theoretical, observational and instrumental astronomy and astrophysics. ... The Astronomical Journal is a monthly scientific journal published by the University of Chicago Press on behalf of the American Astronomical Society. ...

Articles

• Odenwald, S. & Fienberg, RT. 1993; "Galaxy Redshifts Reconsidered" in Sky & Telescope Feb. 2003; pp31–35 (This article is useful further reading in distinguishing between the 3 types of redshift and their causes.)
• Lineweaver, Charles H. and Tamara M. Davis, "Misconceptions about the Big Bang", Scientific American, March 2005. (This article is useful for explaining the cosmological redshift mechanism as well as clearing up misconceptions regarding the physics of the expansion of space.)

Scientific American is a popular-science magazine, published (first weekly and later monthly) since August 28, 1845, making it the oldest continuously published magazine in the United States. ...

Book references

• Binney, James; and Michael Merrifeld (1998). Galactic Astronomy. Princeton University Press. ISBN 0-691-02565-7. 
• Carroll, Bradley W. and Dale A. Ostlie (1996). An Introduction to Modern Astrophysics. Addison-Wesley Publishing Company, Inc.. ISBN 0-201-54730-9. 
• Feynman, Richard; Leighton, Robert; Sands, Matthew (1989). Feynman Lectures on Physics. Vol. 1. Addison-Wesley. ISBN 0-201-51003-0. 
• Grøn, Øyvind; Hervik, Sigbjørn (2007). Einstein's General Theory of Relativity. New York: Springer. ISBN 978-0-387-69199-2. 
• Kutner, Marc (2003). Astronomy: A Physical Perspective. Cambridge University Press. ISBN 0-521-52927-1. 
• Misner, Charles; Thorne, Kip S. and Wheeler, John Archibald (1973). Gravitation. San Francisco: W. H. Freeman. ISBN 0-7167-0344-0. 
• Peebles, P. J. E. (1993). Principles of Physical Cosmology. Princeton University Press. ISBN 0-691-01933-9. 
• Taylor, Edwin F.; Wheeler, John Archibald (1992). Spacetime Physics: Introduction to Special Relativity (2nd ed.). W.H. Freeman. ISBN 0-7167-2327-1. 
• Weinberg, Steven (1971). Gravitation and Cosmology. John Wiley. ISBN 0-471-92567-5. 
• See also physical cosmology textbooks for applications of the cosmological and gravitational redshifts.

Cover of the book on quantum mechanics The Feynman Lectures on Physics, by Richard Feynman, Robert Leighton, and Matthew Sands is perhaps Feynmans most accessible technical work, and is considered a classic introduction to modern physics, including lectures on mathematics, electromagnetism, Newtonian physics, quantum physics, and even the relation... John Archibald Wheeler (July 9, 1911–April 13, 2008) was an eminent American theoretical physicist. ... This article is about the physics subject. ...

External links

Wikimedia Commons has media related to:

Redshift

• Ned Wright's Cosmology tutorial
• Article on redshift from SPACE.com
• Cosmic reference guide entry on redshift
• Mike Luciuk's Astronomical Redshift tutorial