On this day, in 1934, John Norris Bahcall was born. Bahcall’s most widely recognized contribution to astrophysics was his calculation of the number of neutrinos arriving on Earth from the Sun. Neutrinos are subatomic particles and interact very weakly with matter. Bahcall and Raymond Davis Jr. proposed that such neutrino flux would help describe the age, temperature and energy generated by the Sun. This work led to experiments to detect and measure this neutrino flux. The measured values were much lower than the ones predicted by the models of the internal structure of the Sun. This discrepancy was only solved in 2002 after modifications in the theories of neutrinos. Bahcall had also a major role in planning and advocating for the Hubble Space Telescope in the 1970s.