The center of the sun is about 27,000,000°F (15,000,000°C). The surface, or photosphere, of the sun is about 10,000°F (5,500°C). Magnetic anomalies in the photosphere cause cooler regions that appear to be darker than the surrounding surface. These sunspots are about 6,700°F (4,000°C). The sun’s layer of lower atmosphere, the chromosphere, is only a few thousand miles thick. At the base, the chromosphere is about 7,800°F (4,300°C), but its temperature rises with altitude to the corona, the sun’s outer layer of atmosphere, which has a temperature of about 1,800,000°F (1,000,000°C).