What is a Redshift and How to Observe it
The phenomenon in which the observed light has a longer wavelength compared to the wavelength of the emitted light is called redshift. Let's assume that a light source emits light of wavelength λ0. If the observer sees this light with a wavelength of λ where λ>λ0, then we have a redshift. The opposite phenomenon in which the wavelength appears shorter to the observer is called blueshift.
The measure of this increase in wavelength is symbolized as z and can be calculated by the following equation:
z = (λο / λe) - 1
λο: is the wavelength of the observed light
λe: is the wavelength of the emitted light
The positive z value denotes a redshift, while a negative z value denotes a blueshift.
Astronomical redshift can be observed due to three phenomena:
a) The Doppler effect caused by the relative motion betwwen the source and the observer,
b) The effect of high density gravitational fields and
c) The expansion of the Universe still occurring after the Big Bang.
At the left of the image above, we can see the absorption lines of the Sun in the optical spectrum, as they are compared to the absorption lines of a galaxy supercluster (BAS11) at the right. The redshift is evident.