Creating the Microwave Background

Figure 8 : An illustration of how the microwave background was created. Time goes from left to right, and distance from us goes from right to left. The critical change occurs at 380,000 years when the cosmic gas cools enough to change from ionized (foggy) to neutral (transparent). The orange glow from this hot gas we see as microwaves after it is redshifted (stretched) by about a factor of 1000.