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by A RED on April 27th, 2007

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What is red shift & blue shift of a star?

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  • by anonymous on April 27th, 2007

    anonymous

    In physics and astronomy, redshift occurs when the electromagnetic radiation, usually visible light, that is emitted from or reflected off of an object is shifted towards the 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.

    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, 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.

    Another redshift mechanism is the expansion of the universe, which explains the famous observation that the spectral redshifts of distant galaxies, quasars, and intergalactic gas clouds increase in proportion to their distance from the observer. This mechanism is a key feature of the Big Bang model of physical cosmology.[3]

    Yet a third type of redshift, the gravitational redshift (also known as the Einstein effect), is a result of the time dilation that occurs near massive objects, according to general relativity.[4]

    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 very different physical and mathematical descriptions that can lead to a shift in the frequency of electromagnetic radiation and whose action may occasionally be referred to as a "redshift", including scattering and optical effects (for more see section on physical optics and radiative transfer).

    Comments

    • You beat me to it. Please cite sources.

      RamJamBumbleBee

      by RamJamBumbleBee on April 27th, 2007

    • yes, simpler:

      light leaving a distant galaxy would leave at different wavelengths depending on the velocity of the galaxy. if it moves towards the observer, then the wavelength shortened and produce blue, if it moves away then red is produce because wavelength widened. however the speed of light is constant at roughly 299 792 458 m / s.

      Simply Pengu

      by Simply Pengu on November 9th, 2010

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