The northern lights are charged particles caused by storms on the sun. Most of the time they appear as greenish-white colors as oxygen atoms are excited, but sometimes bluish, purplish, and even reddish tinges will appear when the particles react with various states of nitrogen in our atmosphere.

This is a great time of year to watch for the aurora borealis, otherwise known as the northern lights. Actually, aurora don't really favor one season over another, but you have the best chance to see them this time of year simply because the nights are so much longer.

I wish the northern lights were a more predictable phenomenon, and to a certain degree they are, but aurora are still what I call the wild cards of the night sky.

That's because they are ultimately caused by storms on our closest star, the sun. The sun's 10,000 degree F surface is a caldron of chaos. There are constant storms going on, resulting in sunspots, flares, and at times, really large storms called coronal mass ejections, which fling out huge eruptions of highly charged protons and electrons.

These charged particles move like celestial bats out of solar hell at speeds of millions of miles an hour. At times the Earth finds itself in the path of these particles and that's when auroras arrive in our skies.

Since coronal mass ejections are impossible or at best very difficult to predict, it's hard to know when we'll see northern lights. The only thing that we do know for sure is that the sun goes through an 11-year cycle of solar turbulence and storms.

Right now the sun is coming out of the minimum part of that cycle, so the chance of seeing the northern lights will increase in the next few years.

When these charged particles reach the vicinity of our planet, the magnetic field of the Earth directs these particles toward both the north and south geomagnetic poles.

These poles don't exactly coincide with the terrestrial poles but they're close. The northern geomagnetic pole is in far northern Canada. That's why we see more northern lights in the northern part of United States than in the South.

Once these charged particles get to within 70 to 100 miles of Earth's surface, they work their magic with our atmosphere.

They temporarily disrupt the structure of atoms and molecules, resulting in the discharge of light. As billions and billions and billions of collisions occur, the brilliant colors of the aurora dazzle us surface dwellers.

Most of the time we see greenish white colors as oxygen atoms are excited, but sometimes bluish, purplish, and even reddish tinges will appear when the charged particles react with various states of nitrogen in our atmosphere.

Northern lights seem to float across the sky in waves and curtains as they follow the lines of Earth's magnetic field. Most of the time northern lights are restricted to the northern part of the sky, but during really active displays they can spread all over the heavens.

There are several good Web sites you can check that will give some fairly reliable short-term forecasts of aurora. My favorite is from the University of Alaska Geophysical Institute. The web address is www.gi.alaska.edu/aurora_predict/worldmap6.htmle=20061104

This usually works well, but I have to tell you that some of the best displays I've seen were completely unexpected, and some of the ones predicted never really panned out.

To me, that's what makes aurora so much fun. They're the wild cards of stargazing.

Mike Lynch is an amateur astronomer and professional broadcast meteorologist for WCCO Radio in Minneapolis and author of the book, "Pennsylvania Starwatch", available at bookstores and at his website www.lynchandthestars.com.