(1) The Sun is composed primarilyof hydrogen and helium;they account for 74.9% and23.8% of the mass of the Sunin the photosphere, respectively.All heavier elements, calledmetals in astronomy, accountfor less than 2% of the mass,with oxygen (roughly 1% of theSun’s mass), carbon (0.3%),neon (0.2%), and iron (0.2%)being the most abundant.