Introduction
The Sun is a natural nuclear fusion reactor, powered by a proton–proton chain reaction which converts four hydrogen nuclei (protons) into helium, neutrinos, positrons and energy. The excess energy is released as gamma rays and as kinetic energy of the particles and as neutrinos — which travel from the Sun's core to Earth without any appreciable absorption by the Sun's outer layers.
As neutrino detectors became sensitive enough to measure the flow of neutrinos from the Sun, it became clear that the number detected was lower than that predicted by models of the solar interior. In various experiments, the number of detected neutrinos was between one third and one half of the predicted number. This came to be known as the solar neutrino problem.
Read more about this topic: Solar Neutrino Problem
Famous quotes containing the word introduction:
“For better or worse, stepparenting is self-conscious parenting. You’re damned if you do, and damned if you don’t.”
—Anonymous Parent. Making It as a Stepparent, by Claire Berman, introduction (1980, repr. 1986)
“My objection to Liberalism is this—that it is the introduction into the practical business of life of the highest kind—namely, politics—of philosophical ideas instead of political principles.”
—Benjamin Disraeli (1804–1881)
“The role of the stepmother is the most difficult of all, because you can’t ever just be. You’re constantly being tested—by the children, the neighbors, your husband, the relatives, old friends who knew the children’s parents in their first marriage, and by yourself.”
—Anonymous Stepparent. Making It as a Stepparent, by Claire Berman, introduction (1980, repr. 1986)