INSIDE THE SUN Our Nearest Star, The Sun, is a huge globe of hot gas. It is 109 times the diameter of planet Earth and has a mass 745 times bigger than all the planets in the Solar System put together. Without the continuous warming rays of our Sun there would be no life at all on Earth. The source of the Suns scorching heat is a huge nuclear furnace deep beneath the Suns photosphere. It has been blazing for about 4.6 billion years and will continue to burn for about the same time again until its hydrogen and helium fuel runs out.
The suns energy is generated in the core, where it is so hot-15 million °C-that atoms of gas are ripped apart, leaving just their bare nuclei, or centers. The energy travels through the radiative zones to the surface, or photosphere, where it leaves the Sun, mostly as light and infrared radiation. On the way, it passes through the Suns atmosphere, which extends millions of kilometers into space.
At the Suns core, energy is released as hydrogen changes into helium during nuclear fusion reactions. Four hydrogen nuclei (protons) fuse, or join together, to make one helium nucleus. Particles called positrons and neutrinos are released, along with packets of radiation energy called gamma-ray photons.
JOURNEY OF A PHOTON
Aphoton of radiation from the core takes 30,000 years to reach the surface. It collides with gas particles, giving it a random path. At each collision, the photon loses energy and may split into many more photons. Starting as a gamma ray in the core, it emerges from the surface the as a burst of visible light.
Neutrinos produced by nuclear reactions in the Suns core travel out into space. Most of these ghostly particles pass through the earth, but neutrino telescopes can detect a few. The Sudbury Neutrino Observatory, Canada, is 2 km underground to protect it from cosmic rays, which would affect its measurements. Astronomers are puzzled because they find less than half the number of neutrinos they expect.
The photosphere - the Suns surface moves up and down in complex patterns of vibration. Most of these vibrations, of solar oscillations, are caused by sound waves generated below the surface in the convective zone and trapped inside the Sun. By carefully mapping the vibration patterns of the photosphere, scientists can work out the Suns internal structure.
Some solar oscillations may be caused by sunquakes. These are shock waves that spread out from the edges of turbulent circulations of hot gas called convection cells. The energy carried by the shock waves is equal to the energy that would be released by detonating 1.2 billion tonnes of high explosive.
The Suns outer layers are 73 per cent hydrogen, 25 per cent helium, and 2 per cent other elements. In the core, where more than 600 million tonnes of hydrogen are converted into helium every second, the amount of hydrogen is only about 34 per cent, while the amount of helium is about 64 per cent.