It turns out that just like for sound waves, the wavelength of light emitted by an object that is moving away from you is longer when you measure it than it is when measured in the rest frame of the emitting object. The Doppler effect can happen for light waves too (though it can't be properly understood without knowing special relativity). You've experienced the Doppler effect if you've ever had a train go past you and heard the whistle go to a lower pitch (corresponding to a longer wavelength for the sound wave) as the train moves away. In fact, only in the first case (a nearby body moving away from the earth) is the redshift caused by the Doppler effect. But there's a subtle difference, which you sort of allude to.
its wavelength will be stretched, so the color of the light is more towards the red end of the spectrum. In both cases, the light emitted by one body and received by the other will be "redshifted" - i.e. Since frequency and wavelength are inversely proportional, this is equivalent to saying that the frequency of the light is reduced towards the red part of the light spectrum, giving this phenomenon the name redshift.If a body was launched from earth reaching a high constant velocity away from earth, in what way would the Doppler effect between earth and that departing body be any different than any Doppler effect between the earth and a distant body moving away from earth at the same velocity due only to the expansion of space? To this layman, it seems that in the case of the body launched from earth, the Doppler effect results from the waves having to deal with the rapid and constant increase in the units of space between the two bodies (not to the expansion of those units of space separating them) while in the case of the distant body, any Doppler effect would be affected by the expansion of the units of space through which those waves were traveling (not to the addition of units of space between them). If applied to optical wavelengths, this manifests itself as a change in the colour of visible light as the wavelength of the light is increased toward the red part of the light spectrum. There also exists a corresponding blueshift when electromagnetic radiation propagates from an area of a weaker gravitational field to an area of a stronger gravitational field. There is a corresponding reduction in energy when electromagnetic radiation is red-shifted, as given by Planck's relation, due to the electromagnetic radiation propagating in opposition to the gravitational gradient. As frequency is inverse of time, frequency of the electromagnetic radiation is reduced in an area of a higher gravitational potential. This is a direct result of Gravitational time dilation - as one moves away from a source of gravitational field, the rate at which time passess is increased relative to the case when one is near the source. In astrophysics, gravitational redshift or Einstein shift is the process by which electromagnetic radiation originating from a source that is in gravitational field is reduced in frequency, or redshifted, when observed in a region of a weaker gravitational field. Freebase (0.00 / 0 votes) Rate this definition: