Motion Relative to the CMB

The following image was constructed from COBE data. It shows the temperature of the cosmic microwave background plotted in galactic coordinates, with red cooler and blue and violet hotter. This dipole anisotropy is because of the Doppler effect (see the right frame). If the Earth moves with respect to the microwave background, the radiation will be blueshifted to a higher effective temperature in the direction of the Earth's motion and redshifted to a lower effective temperature in the direction opposite the Earth's motion.

The indication of the above image is that the local group of galaxies, to which the Earth belongs, is moving at about 600 km/s with respect to the background radiation. It is not known why the Earth is moving with such a high velocity relative to the background radiation.