A HOT HEART
Solar astronomers use a technique called helioseismology to look below the surface of the Sun. Using telescopes positioned around the Earth (to keep the Sun under Hconstant watch), they study subtle pulsations in the Sun's surface. These pulsations— essentially sound waves— probe the Sun's interior in much the same way that seismic waves from earth-quakes enable geophysicists to study our planet.
Such studies have shown that the Sun has a layered structure. The core extends outward to about quarter of the Sun's radius, containing merely 7 percent of the volume, but half the mass, of the Sun. It has a temperature of some 27 million degrees Fahrenheit (15,()()(),()()()° C). The core is the "engine room" of the Sun, where the energy released from nuclear fusion streams outward. This energy is carried by radiation in the form of photons, which are parcels of electromagnetic energy.
Three-quarters of the way to the surface, the solar |gas becomes considerably cooler and undergoes a boiling, convective motion. Convection carries the core's energy along the last step outward. Just below the photosphere—the visible surface—the big upwelling cells of gas break down into smaller ones. resulting in the granules seen on the surface. By the time it readies the photosphere, the gas has cooled to about 1.000 degrees Fahrenheit (6,000° C).