How a big star (Sun) makes energy and heat What happens in the core of the sun How Sun(big star) produce Heat. The Sun is an incredibly massive and powerful star that produces an enormous amount of heat and light through a process called nuclear fusion. Here are some highlights and facts about how the Sun makes heat: • The Sun is made up mostly of hydrogen, with some helium and other elements. • In its core, temperatures reach up to 15 million degrees Celsius, which is hot enough to sustain nuclear fusion reactions. • Nuclear fusion is a process in which atomic nuclei combine to form heavier elements, releasing energy in the process. In the case of the Sun, hydrogen atoms are fused together to form helium, releasing massive amounts of energy in the form of heat and light. • The fusion process in the Sun's core is incredibly efficient, converting about 4 million tons of matter into energy every second. • The energy produced by nuclear fusion in t...