The core starts from the center and extends outward to encompass 25 percent of the sun's radius. Its temperature is greater than 15 million degrees Kelvin [source: Montana]. At the core, gravity pulls all of the mass inward and creates an intense pressure. The pressure is high enough to force atoms of hydrogen to come together in nuclear fusion reactions -- something we try to emulate here on Earth. Two atoms of hydrogen are combined to create helium-4 and energy in several steps:
- Two protons combine to form a deuterium atom (hydrogen atom with one neutron and one proton), a positron (similar to electron, but with a positive charge) and a neutrino.
- A proton and a deuterium atom combine to form a helium-3 atom (two protons with one neutron) and a gamma ray.
- Two helium-3 atoms combine to form a helium-4 atom (two protons and two neutrons) and two protons.
These reactions account for 85 percent of the sun's energy. The remaining 15 percent comes from the following reactions:
- A helium-3 atom and a helium-4 atom combine to form a beryllium-7 (four protons and three neutrons) and a gamma ray.
- A beryllium-7 atom captures an electron to become lithium-7 atom (three protons and four neutrons) and a neutrino.
- The lithium-7 combines with a proton to form two helium-4 atoms.
The helium-4 atoms are less massive than the two hydrogen atoms that started the process, so the difference in mass is converted to energy as described by Einstein's theory of relativity (E=mc²). The energy is emitted in various forms of light: ultraviolet light, X-rays, visible light, infrared, microwaves and radio waves.
The sun also emits energized particles (neutrinos, protons) that make up the solar wind. This energy strikes Earth, where it warms the planet, drives our weather and provides energy for life. We aren't harmed by most of the radiation or solar wind because the Earth's atmosphere protects us.