Much like the Earth, the Sun has different layers to its structure. The densest region is located at the middle, where hydrogen and helium are being pulled to the center of the Sun by gravity. Light particles (a.k.a. photons) produced in the core by nuclear fusion have to reach the layer known as the photosphere before escaping into space. After their valiant escape, it takes just 8 minutes for the photons to hit the Earth. The photosphere is the “surface” of the sun that we see with our eyes (using proper eye protection, of course!) Photons can spend thousands of years trying to escape the dense inner layers before finally reaching the photosphere.
Outside the photosphere are two areas known as the chromosphere and the corona that will be visible during the eclipse. Usually you cannot see these regions at all. They are too close to the intense light of the photosphere, and their light gets outshone. The chromosphere is a small red layer that is cooler than the photosphere. It will actually appear as a red or pink ring during the eclipse. The corona is a large sparse cloud of hot solar material. The corona is unusually hot, at about 1000 times hotter than the photosphere (1,800,000 °F.) Scientists do not know what the causes the corona to be so incredibly hot. The corona will be seen as wispy strands of white material coming out from behind the Moon.