Final answer:
The degree of red and blue shift at a star's edges depends on its speed of rotation. This phenomenon is used by astronomers to measure a star's rotational speed through the Doppler effect and line broadening.
Step-by-step explanation:
The degree of red and blue shift occurring at the outside edges of a rotating star depends on its speed of rotation. The Doppler effect is responsible for this shift, with one side of the star moving towards us being blue-shifted and the opposite side moving away being red-shifted. This effect, known as line broadening, helps astronomers determine the rotational velocity of a star. For galaxies, the red shift observed is largely due to the expansion of space, which is evident from the increasing red shifts with greater distances, indicating an expanding universe.