Solar interior

Solar energy is created deep within the core of the Sun. The temperature (15.7 million degrees, maybe lower see below) and density (151 g/cm3 ) are so high that nuclear reactions ( 41H + 2e -- 4He + 2 neutrinos + 6 photons ) can take place. Each He nucleus is smaller in mass by 3% than the original protons and this difference is converted to energy according to Einstein's equivalence E = mc2. The energy is then carried to the solar surface (photosphere) where it is released as light and heat. A small part of that energy produces the magnetic fields.

By analyzing the weak, complex throbbing motions that cover the solar surface, it has become possible to study the solar interior. The spacecraft SOHO has on board three instruments (MDI/SOI, VIRGO, GOLF) which can study these oscillations. Remarkable results have been obtained by the Solar Oscillation Investigation (SOI) group at Stanford University. The SOI group uses the Michelson Doppler Imager (MDI) on board the SOHO spacecraft.

Physical quantity derived from helioseismological studies