Rather than coal, the Sun is about composed of about 3/4 hydrogen and 1/4 helium. When hydrogen atoms are forced by high pressure and temperature to combine into heavier helium atoms, some mass is lost in the process. That "lost" mass is converted to energy equivalent to mc2, according to Einstein's famous equation. Since c (the speed of light) is a large number, a small amount of mass gets converted into a large amount of energy. This process is called hydrogen fusion, and is the same energy source used in hydrogen bombs.
The Sun converts almost 600 million tons of hydrogen to helium in its core each second, but it is estimated that there is enough hydrogen fuel in the Sun for it to shine for another 5 billion years.
Answered by: Paul Walorski, B.A., Part-time Physics/Astronomy Instructor
Our server costs have gone up and our advertising revenue has gone down. You do the math! If you find our site useful, consider donating to keep us going. Thanks!
'To myself I seem to have been only like a boy playing on the seashore, and diverting myself in now and then finding a smoother pebble or a prettier shell than ordinary, whilst the great ocean of truth lay all undiscovered before me.'