The light from the East limb (edge) of the Sun is blue shifted and the light from the West limb is redshifted. This is because
a) different kinds of atoms emit light at the opposite edges.
b) the Sun is rotating.
c) the distance from the Sun to Earth changes.
d) the two sides of the Sun are at different temperatures.
Answer: b) the Sun is rotating.
One edge is a "source moving towards" us and the other edge is a "source moving away" from us.