PHYSICS · Single correct · A Level · Physics · Astrophysics · Astrophysics
Problem
Light from star X is observed to be blue-shifted. Light from star Y is observed to be red-shifted. What is the most likely reason for this?
(1) Star X is hotter than star Y.
(2) Star Y is hotter than Star X.
(3) Star X is moving away from us and star Y is moving towards us.
(4) Star X is moving towards us and star Y is moving away from us.