How does the sun shine? The sun shines by burning hydrogen into helium in its core. This process is called nuclear fusion. Fusion happens when lighter elements are forced to become heavier elements. When this happens, a tremendous amount of energy is created. The famous scientist Albert Einstein discovered a formula which shows how much energy can be created from a small amount of mass. You may have heard of the famous formula E=mc2. E is energy, m is mass, and c is the speed of light. The speed of light is 186,000 miles or 300,000 km per second. So you can see that a tiny amount of matter can be changed into an enormous amount of energy. This can only happen in places which have extremely high pressures and temperatures. At the center of the sun, the temperature reaches 16 million degrees K, and the pressure is more than a billion times the atmospheric pressure on Earth! The sun converts about 5 million tons of mass into energy every second. This energy heats the sun, and in turn, the sun heats Earth and all the other planets.