When the gases in Earth's atmosphere interact with the perpetual stream of particles flowing from the Sun, luminous colors and shapes can be seen in the dark skies near Earth's magnetic poles. This is called the Aurora Borealis (at the North pole) and the Aurora Australis (at the South pole). Although auroras are always present in some form, they vary in intensity, and often they are either too faint to be seen or are obscured by or clouds or daylight.

The solar wind carries this stream of particles through the solar system, dragging the interplanetary magnetic field (IMF) with it. The IMF is the magnetic field produced by the Sun, similar to Earth's magnetosphere but much larger. Typically, the magnetosphere surrounds and protects the Earth by deflecting most of the solar wind. However, when the IMF and the magnetosphere interact, some solar particles are able to leak in along the magnetic field lines at the North and South Poles, causing auroras.

When high-energy particles from the solar wind collide with gases in Earth's upper atmosphere, the gases are excited. Through the same process that makes a neon sign glow, excited gas particles temporarily gain energy. When they drop back to their regular energy levels, the released energy can be seen as light in the aurora.

While the sun appears to shine at a constant rate, it really does not. At time dark spots (sunspots) appear on its surface. These sunspots, surrounded by particularly bright areas are caused by the sun's magnetic field. During periods of high solar activity the magnetic field produces more sunspots than usual and the sun shines just a little bit brighter.

The sun's magnetic field reverses every 22 years, and the sunspot cycle reaches a maximum every 11 years. Scientists have connected periods of low solar activity - times with less sunspots - to climate change. They also noticed that when there was lower solar activity and less sunspots, the auroras were also more rare.



Sources
Teachers' Domain, Gallery of Auroras, published October 21, 2005, retrieved on November 5, 2009, http://www.teachersdomain.org/resource/ess05.sci.ess.eiu.auroras/ (fair use)
Teachers' Domain, Solar Magnetism, published December 17, 2005, retrieved on November 5, 2009, http://www.teachersdomain.org/resource/ess05.sci.ess.eiu.magnetism/ (fair use)