What is a REDSHIFT... as it applies to astronomy?

Answer 1

A redshift is a shift in the frequency of a photon toward lower energy, or longer wavelength. The redshift is defined as the change in the wavelength of the light divided by the rest wavelength of the light, as ...
In physics and astronomy, redshift occurs when the visible light from an object is shifted towards the red end of the 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 blueshift.

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.

A redshift can occur when a light source moves away from an observer, corresponding to the Doppler shift that changes the frequency of sound waves. Although observing such redshifts 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 Doppler redshift phenomenon was first predicted and observed in the nineteenth century as scientists began to consider the dynamical implications of the wave-nature of light.

Another redshift mechanism accounts for the famous observation that the spectral redshifts of distant galaxies, quasars, and intergalactic gas clouds are observed to increase proportionally with their distance to the observer. This relation is accounted for by models that predict the universe is expanding, seen in, for example, the Big Bang model.[3] Yet a third type of redshift, the gravitational redshift also known as the Einstein effect, results from the time dilation that occurs in general relativity near massive objects.[4]

The history of the subject begins with the development in the nineteenth 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 first Doppler redshift was described by French physicist Armand-Hippolyte-Louis Fizeau in 1848 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]

In 1871, optical redshift is confirmed when the phenomenon is observed in Fraunhofer lines using solar rotation, about 0.1 Å in the red.[citation needed] [9] In 1901 Aristarkh Belopolsky verified optical redshift in the laboratory using a system of rotating mirrors.[10]

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]

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 are today considered strong evidence for an expanding universe and the Big Bang theory.[15]


[edit] Measurement, characterization, and interpretation
A redshift can be measured by looking at the spectrum of light that comes from a single source (see idealized spectrum illustration top-right). If there are features in this spectrum such as absorption lines, emission lines, or other variations in light intensity, then a redshift can in principle be calculated. This requires comparing the observed spectrum to a known spectrum with similar features. For example, the atomic element hydrogen, when exposed to light, has a definite signature spectrum that shows features at regular intervals. If the same pattern of intervals is seen in an observed spectrum occurring at shifted wavelengths, then a redshift can be measured for the object. Determining the redshift of an object therefore requires a frequency- or wavelength-range. Redshifts cannot be calculated by looking at isolated features or with a spectrum that is featureless or white noise (random fluctuations in a spectrum).[16]

Redshift (and blueshift) 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: @ http://en.wikipedia.org/wiki/Redshift

After z is measured, the distinction between redshift and blueshift is simply a matter of whether z is positive or negative. According to the mechanisms section below, there are some basic interpretations that follow when either a redshift or blueshift is observed. For example, Doppler effect blueshifts (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, Einstein effect blueshifts are associated with light entering a strong gravitational field while Einstein effect redshifts imply light is leaving the field.

Answer 2

Redshift applies to the Dopple effect, in that the APPARENT wavelength of a wave is altered by whether the wave is approaching or receding an observation point. As objects move AWAY from an observation point, there is a shift in the appearance of the light waves toward the shorter wavelengths (red in the visible light spectrum). If an object was moving TOWARD the observation point, the light waves would appear longer (blue).

Short version: the change in light coming frrom various stars has 'shifted' more toward red over years of observation, which means these stars are moving away from us. The conept of Redshift in astronomy is the key principle that has led to the development of the "Big Bang" theory and the spreading of the universe.

Hope that helped.

Answer 3

First of all, in physics and astronomy, redshift is an observed increase in the wavelength and decrease in the frequency of electromagnetic radiation received by a detector compared to that emitted by the source. For visible light, red is the color with the longest wavelength…..And.. The REDSHIFT of an object is the amount by which the spectral lines in the source are shifted to the red. That is, the wavelengths get longer. In other words and in brief… a redshift is an increase in the wavelength of radiation emitted by a celestial body as a consequence of the Doppler effect,,,, for a GREAT synopsis of redshift.. go to that website below.. It is GREAT and much more descriptive in nature with the colors , etc.

Answer 4

When objects like Galaxies move/accelerate away from the Earth, they take get redshifted which means more red light gets to us as it's wavelength is increased. Blue shift is the oppostite...

Answer 5

An example of the red shift [the Doppler effect] When a siren approaches and passes,you hear one pitch as it approaches and a shorter one when it passes.
The red shift in astronomy indicates,by comparison which of two objects is receding faster than the other.

Answer 6

All stellar objects are moving away from us as observers (wherever we might be) and the frequency of light is elongated, which means shifted towards the red end of the spectrum. The faster the object is moving away, the longer the shift, the redder the light appears.

Answer 7

moving away, when an object in space moves away very quickly then its frequency downshifts this is called an Doppler shift when it approaches its a blue shift . just like when you hear a car driving away it sounds lower in pitch because the sound waves are being stretched. as it approaches it sounds higher but as it goes by it goes down in pitch.

Answer 8

it has to deal with how large object in space are moving if they move away, it affects the red side of the spectrum, towards, the blue side

Answer 9

i dont know