Jodi Robokoff, age 11, of Casper, Wyo., for her question:

WHICH STAR IS THE BRIGHTEST?

The brightest star in the heavens, excluding the sun, is Sirius. It is often called the Dog Star. Although it is one of the stars nearest to earth, it is still so far away that its light takes about nine years to reach the earth.

Sirius is a star of the first magnitude and it radiates about 30 times as much light as does the sun. Astronomers discovered its companion star in 1862. The two stars move around each other as they travel through space.

You can see the Dog Star by looking along an imaginary line pointing southward through Orion's belt. It is the head of the constellation Canis Major, the Great Dog.

The Dog Star's companion was the first white dwarf star discovered. Many more white dwarfs have since been found, some with densities 500,000 times that of water.