Jim Wilmington, age 15, of Concord, N.H., for his question:

HOW BIG IS THE UNIVERSE?

The universe consists of all the matter, light and other forms of radiation and energy that have been discovered by humankind. The universe also consists of everything that we believe to be present somewhere in time and space.

Earth and everything on it as well as everything in the solarsystem is included in the universe. All of the stars, of which the sun is one, are part of the universe. More than 100 billion stars are grouped in the shape of a giant circular galaxy called the Milky Way. The Milky Way, our galaxy, is about 100,000 light years across. A light year is the distance that light travels in a year: about 5.88 trillion miles.

Studies indicate that there are at least as many additional galaxies in the universe as there are stars in the Milky Way.

Most astronomers think that quasars, which emit immense quantities of light and radio waves, may be the oldest and most distant objects in the universe. Quasars may be as far away as 10 billion light years from earth.