The magnitude of the wavelength change in a spectrum caused by the
Doppler effect.
A Doppler shift in the spectrum of an astronomical object is commonly described as a
redshift when it is towards longer wavelengths
(object receding) and as a blueshift
when it is towards shorter wavelengths (object approaching). Its magnitude,
z,
is quantified in terms of the ration of the wavelength change, Dl,
to the original wavelength l,
since the theory shows that this quantity is a constant determined by
the velocity of separation, v,
between the object and its observer. When v is small in relation to the velocity of
light, c, Dl/l = v/c.
If v is a significant
fraction of c, a formula derived from Special Relativity
theory must be used:
(1998).ISO/media/astdict/d/graphics/dshift.jpg)
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