[OAB 95] It is claimed that the Sun might not be operating by thermonuclear fusion at all, in which case the Sun would not have an energy source powerful enough to last for 4.5 billion years. The main reason for thinking this was that the amount of neutrinos (a sub-atomic particle) coming out of the Sun was only about a quarter of what was theoretically expected. Firstly, the existence of a significant flow of neutrinos cannot be explained by any method other than nuclear processes; so even though the theory needed refining, it was extremely over-zealous to claim that the difficulty disproves fusion in the Sun (to be fair, some people merely claimed that the lack of neutrinos showed that fusion could not account for all of the Sun's energy). But secondly, the necessary adjustments have now been made to the theory due to the recent experimental proof that the neutrino is not a massless particle like a photon, but instead it has a tiny mass like an electron does. With this adjustment, nuclear theory now correctly accounts for the Sun's neutrino flow, and there is no reason to doubt that nuclear fusion is the source of all the Sun's energy.