Practise explaining how observed galactic redshift, compared with known spectral lines, provides evidence that the Universe is expanding and galaxies are receding.
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.
wavelength has increased / light is redshifted
B1
star within galaxy is moving away / receding (from Earth)
B1
Universe is expanding
B1