Arnold Boyle, age 11, of Bowling Green, Ohio, for his question:

HOW BIG IS THE UNIVERSE?

The universe is made up 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 space and time.

More than 100 billion stars are grouped in the shape of a giant circular galaxy, our own, called the Milky Way. The Milky Way is about 100,000 light years across. A light year is the distance that light travels in a year, about 5.88 trillion miles.

To try to understand how big the universe is, consider this fact: Scientists tell us there are at least as many galaxies in the universe as there are stars in the Milky Way. That means more than 100 billion galaxies, many about 100,000 light years across.

That's big.