Why does the Sun shine?
It was believed long ago that the Sun shines because of the light emerging from the burnt coal in the Sun. If that is the case, scientists have calculated that the amount of light that comes out of such a big mass of coal would last for only a few thousands of years. But, according to Darwin’s calculation, it is more than 300 million years since the earth started its existence.‚ He also said that the biological processes and evolution also started from that time Lord Kelvin has calculated the period of the Sun’s activity on earth to have started around 30 million years ago. Kelvin has indicated firmly that the largest and most efficient energy source of the Sun, whichever it may be, can provide light for the maximum of 30 million years. By this time, the coal theory had totally vanished. After a lot of study made by several scientists in this regard, we now know that the Sun and Earth are about 5 billion years old.
Arthur Eddington has proposed that conversion of hydrogen to helium might result in the release of energy that can indicate the age of the Sun, determined by Darwin. Albert Einstein, in 1905, found that there is a relation between mass and energy. His theory has extended the law of conservation of energy given by Helmholtz. Another discovery by F.W. Aston, that four hydrogen nuclei were found to be heavier than helium, actually started the solution to the question why and how the Sun shines.
Later in the 1960’s, Hans Bethe found the type of nuclear reaction that occurs in stars. He came out with the resultant reaction that is known to occur even in the Sun. He added four hydrogen nuclei to four protons to form one helium nucleus, two positrons and two neutrinos. Then Ray Davis said that neutrinos form inside the sun when hydrogen forms helium. The luminosity of the Sun is result of the energy released when hydrogen converts into helium by releasing neutrinos. The details of the reason behind the sunshine is explained vividly in the research paper entitled ‘Energy production in stars’, by Bethe.