ENERGY FROM THE SUN

Our sun is an ordinary star, average in size and brightness, compared to the millions of others in the universe. But when energy from the sun travels through 93 million miles of space in only eight minutes to reach us here on Earth, extraordinary things can and do happen.

How does the sun make energy? The sun is a huge ball-shaped cloud of hot gases held together by gravity. It is made up mostly of hydrogen and helium. Inside the sun, hydrogen atoms moving very quickly collide with one another. Sometimes they combine to make helium atoms in a nuclear process called fusion.

During fusion, a tiny amount of mass is lost. One helium atom weighs just a little bit less than two hydrogen atoms. That little bit of mass is transformed into an enormous amount of energy, mainly infrared and visible light, which radiates in all directions through space.

The sun has been emitting energy constantly for about five billion years. Astronomers estimate it will continue for another five billion.

Only a small fraction of solar radiation (one part in two billion) reaches the earth. Even so, the sun is the source of almost all the energy on earth, including our food and our fuel.

Let's look at the many forms the sun's energy can take.

NEXT: Energy Changes