The effect that makes the cosmic microwave background appear slightly warmer in one direction and cooler in the opposite direction is
A) the focusing effect of the gravitational field of the local galaxy on the radiation.
B) the presence of many extra sources of the radiation in one direction.
C) a basic asymmetry in the background radiation,related to its origin.
D) the Doppler shift,caused by motion of our Galaxy through space toward the constellation Leo.

Question

Quizplus · Accepted Answer

The effect is due to the Doppler shift, which occurs because our galaxy is moving through space. This motion causes the cosmic microwave background radiation to appear slightly warmer in the direction we are moving towards (due to the compression of the radiation wavelengths) and cooler in the opposite direction (due to the stretching of the wavelengths).

The Effect That Makes the Cosmic Microwave Background Appear Slightly