CAIE A-Level Physics A2 25.3.3 Why Redshift Leads to the Idea That the Universe Is Expanding Topic Practice

A spectral line from a star within a galaxy is observed to have a wavelength of 660.9 nm . The same spectral line measured in the laboratory is observed to have a wavelength of 656.3 nm .

State and explain what can be concluded about the Universe based on this change in observed wavelength.