Sue Terrell, age 11, of Harrisurg, Penn., for her question:

WHY DO STARS SHINE?

A star's energy source lies deep within it. There, hydrogen gas changes into helium gas through a process called nuclear fusion. From the surface of the star, the energy passes into space in such forms as light, heat and radio waves.

During the nuclear fusion process, the amount of helium produced does not wholly equal the amount of hydrogen used up. Some of the material that makes up the original hydrogen changes into energy rather than into helium

Nuclear fusion creates so much energy that the temperature at the center of the star reaches millions of degrees. Stars continue to shine until they use up all of their hydrogen. Astronomers say that most stars have enough hydrogen to last billions of years.

Starlight ranges in color from light blue, yellow, orange red to white. The star's color indicates the temperature of its surface.