3. describe how the relative proportion of hydrogen, helium, and heavier elements will change as the sun ages. 4. how does energy release from the sun reach earth? how does the sun's energy interact with earth's atmosphere and hydrosphere? 5. every star starts with an initial mass of hydrogen. each atom of hydrogen has one proton and one neutron. how are the total number of protons and neutrons conserved as a star ages and undergoes continuous nucleosynthesis? 6. what mechanisms or events are needed for a star to make heavier elements than iron? 7. how do scientists use electromagnetic emissions of stars to determine their composition, age, and stage of development?