The weak interaction in the Sun:
The Sun gets its energy from the fusion reaction that transforms two protons into a nucleus of deuterium, a positron and a neutrino. This reaction liberates 2 MeV, and forms the neutrons which will later be used in heavier nuclei. Such processes would be impossible without the phenomenon responsible for the beta decay: the weak interaction. Weak interaction allows a proton to transform during a very short period of time into a W boson and a neutron (1). If, during these short lapses of time, this W boson decays into a neutrino and a positron (2), the neutron can bind itself with an other proton, then forming a deuterium nucleus (3).