Kathy Kosednar, age 11, of Waukesha, Wisconsin, for her question:

Which Northern Hemisphere star is closest to the sun?

This question, of course, means the closest star we can see in our skies north of the equator. Naturally the distance between the sun and a star has nothing to do with our hemispheres. A star's distance from the earth varies slightly as we orbit the sun. But compared with the enormous distances of even the nearest stars, these and other variations are too slight to mention.

When first place is out of reach, a sensible person is content to settle for second place    which is what Kathy's question is all about. The star that is closest to us and the sun cannot be seen in the skies above the Northern Hemisphere. It is visible only south of the equator and we have to settle for the nearest star we can see in our own skies.

Actually, it is the sun's second closest neighbor and it happens to be the brightest star that can be seen from any place on the planet Earth. It is a winter star, and you can't miss it because it belongs in the most dazzling group of stars we ever see.

In the early evening, look for a long thin diamond of dazzling stars. The two brilliant stars at the top and the bottom mark the shoulder and the knee of the constellation Onion, the Hunter. The three smaller stars across the center of the skinny diamond mark the heavenly hunter's belt. Rising after Onion, come two small constellations called Canis Mayor and Canis Minor    Big Dog and Little Dog.

There you will see a bright sparkler, snapping at the heels of Onion. This eye catcher is Sirius, alias the Dog Star    the closest star we see in our Northern Hemisphere skies and the most brilliant star ever seen from any place on the earth. Its distance from the Solar System is about 8.6 light years. This means that light from the big bright sparkler takes almost nine years to get from there to here.

Sirius is quite a bit bigger than our sun and it sheds about 30 times more light. Actually, it is a double star, though its tiny companion was not discovered until about a century ago. It is a little white dwarf star called the Pup    naturally. Small as it is, the Pup is made of super dense material that is 50,000 times heavier than water. On earth, a thimbleful of this heavy star stuff would weigh more than a quarter of a ton. Though no bigger than a large planet, the hot and heavy little dwarf is as massive as a medium sized star.

The Dog Star and the Pup are linked by gravity in a double star system. Sirius barely wobbles while the little dwarf swings around it in a large, oval shaped orbit.

The closest star to the Solar System is Proxima, a red dwarf of the triple star system Alpha Centauri. The triplets shine as one bright star in the skies south of the equator. Their distance is 4.3 light¬ years.