Figure 25-9: Our Motion Through the Microwave Background Because of the Doppler effect, we detect shorter wavelengths in the microwave background and a higher temperature of radiation in that part of the sky toward which we are moving. This part of the sky is the area shown in red in Figure 25-8. In the opposite part of the sky, shown in blue in Figure 25-8, the microwave radiation has longer wavelengths and a cooler temperature.