Pictures courtesy of
Jan Curtis
jcurtis@uwyo.edu
Website: click here

· Auroras occur around Earth's north (aurora borealis) and south (aurora australis) geomagnetic poles in regions known as auroral ovals.

· The aurora is higher in the atmosphere than the highest jet plane flies. The lowest fringes are at least 40 miles above the Earth, while the uppermost reaches of the aurora extend 600 miles above the Earth. The space shuttle flies near 190 miles altitude.

· Auroras occur because Earth's magnetic field interacts with the solar wind, a tenuous mix of charged particles blowing away from the sun. This wind from the sun sweeps by Earth in the interplanetary magnetic field which is produced by the sun.

· Auroral light is similar to light from color television. In the picture tube, a beam of electrons controlled by electric and magnetic fields strikes the screen, making it glow in different colors, according to the type of chemicals (phosphors) that coat the screen. Auroral light is the from the air glowing as charged particles, particularly electrons, rain down along the Earth's magnetic field lines. The color of the aurora depends on the type of atom or molecule struck by the charged particles.

· Auroral displays vary from night to night and during a single night. Usually, if sun-earth conditions produce an auroral substorm, a diffuse patch of glowing sky will be seen first, followed by a discrete arc that brightens, perhaps a thousand-fold in a minute. As an arc moves toward the equator, new ones may form on its poleward side.
Appearing within arcs are upward-reaching striations aligned with the magnetic field, giving the impression of curtains of light. Ripples and curls dance along the arc curtains and pulsating patches of light may appear in the morning hours.