The cosmic microwave background radiation is not uniform over the sky-it is slightly hotter toward the constellation Leo and slightly cooler in the opposite direction, toward Aquarius. Why?
A) The difference is probably a statistical fluctuation and therefore not real.
B) The background radiation really is uniform; the observed difference is due to Earth's motion through the universe.
C) Earth is slightly off-center in the universe, so one side of the universe is a bit closer and the other is a bit farther away.
D) That is the way the universe began-hotter in one direction and cooler in the other.

Question

Quizplus · Accepted Answer

The observed difference in temperature of the cosmic microwave background radiation is due to the Doppler effect as Earth (and our entire solar system) moves through the universe. This motion causes the radiation to appear slightly hotter in the direction of movement (toward Leo) and cooler in the opposite direction (toward Aquarius).

The Cosmic Microwave Background Radiation Is Not Uniform Over the Sky-It