Transcript: At the first step in the proton-proton chain in the Sun and other low mass stars neutrinos are produced. Since neutrinos interact so weakly with ordinary matter they flee the Sun almost instantly. Ten to the fourteen neutrinos pass through every square meter of the Earth’s surface every second. Ten trillion pass through your body every second, and you don’t feel a thing. Getting neutrinos to interact is difficult, so detecting them is an extreme experimental challenge. The best way is to put large tanks of extremely pure fluid deep underground to shield from cosmic rays and look for the exceptionally rare interactions between a neutrino and a particle in the fluid. Essentially a form of cleaning fluid works best. Deep underground mines to detect neutrinos experiments have been in operation for over thirty years. Ray Davis at Brookhaven Lab was the pioneer of this type of experiment. Solar neutrinos have been detected for that length of time which is a profound confirmation that fusion actually does occur in the center of the Sun. Neutrinos allow us to see into the heart of the Sun where fusion actually occurs. However, in detail the rate of occurrence of neutrino interactions was one-third the prediction of standard solar models. This remained an extreme puzzle indicating that perhaps we didn’t understand stellar fusion at all until the discovery relatively recently that neutrinos can oscillate and change their flavor. This explains the shortfall of solar neutrinos.