Solar energy is produced at the center of the star, in its core, where the temperature reaches 15,000,000 ?C and where hydrogen is converted into helium by means of nuclear fusion. In the radiative zone, the energy produced migrates in the form of photons (light particles) and cools down. The photons interact constantly with the matter, following such an irregular path that it takes them more than a million years to emerge from the radiative zone. They then cross the convection zone, where whirls of hot gas circulate between the hotter lower regions and the ¨cooler〃 surface region. When they reach the photosphere, the photons are emitted in the form of light and heat, at a temperature of 6,000 ?C. It takes eight minutes for this light to reach Earth.