The energy from the Sun – both heat and light energy - originates from a nucleaer fusion process that is occurring inside the core of the Sun. The specific type of fusion that occurs inside of the Sun is known as proton-proton fusion. Inside the Sun, this process begins with protons (which is simply a lone hydrogen nucleus) and through a series of steps, these protons fuse together and are turned into helium. This fusion process occurs inside the core of the Sun, and the transformation results in a release of energy that keeps the sun hot. The resulting energy is radiated out from the core of the Sun and moves across the solar system. It is important to note that the core is the only part of the Sun that produces any significant amount of heat through fusion (it contributes about 99%). The rest of the Sun is heated by energy transferred outward from the core.
Figure 1 :::: The proton-proton fusion process that is the source of energy from the Sun ::::