Redshift and speed $c$

Question

If the speed of light in vacuum is constant to every observer then how is the shifting of light color possible?

I am assuming that a single particle of light (a photon?) has the capability to contain a light property. If true then

What is happening to the photon when it is getting color shifted?

bearing in mind that it does not change speed with respect to the observer?

Allure · Accepted Answer

Speed is not the only property of light - there is also frequency, which measures how often the light's electric and magnetic fields oscillate in unit time. It is the frequency that is changing when light is redshifted.

Correct answer by Allure on December 24, 2020

Redshift and speed $c$

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