Auroras: the Northern
and Southern Lights

The aurora, or northern and southern lights, are often visible from the surface of the Earth at high northern or southern latitudes. Auroras typically appear as luminous bands or streamers that can extend to altitudes of 200 miles (well into the ionosphere).

Northern and Southern Lights

The following figures show three examples of the often spectacular visible light display associated with auroras.

Southern aurora from the Space Shuttle Endeavor (Ref) Northern aurora over Lake Superior (Ref) Northern aurora over Circle, Alaska (Ref)

Here is another image of the southern aurora taken from the Space Shuttle. The aurora changes with time, often looking like moving curtains of light. Here are some MPEG and QuickTime film clips that illustrate the time dependence of the auroral display.

The Cause of Auroras

Auroras are caused by high energy particles from the solar wind that are trapped in the Earth's magnetic field . As these particles spiral back and forth along the magnetic field lines, they come down into the atmosphere near the north and south magnetic poles where the magnetic field lines disappear into the body of the Earth.

The delicate colors are caused by energetic electrons colliding with oxygen and nitrogen molecules in the atmosphere. This excites the molecules, and when they decay from the excited states they emit the light that we see in the aurora.

Auroras at Non-Visible Wavelengths

The collisions of trapped charged particles with atmospheric molecules causes spectacular effects in the visible spectrum, but these excited molecules can also emit radiation in other wavelength bands. The following figures show aurora imaged in the ultraviolet (UV) and X-ray regions of the spectrum.

UV emission from northern aurora observed by the Polar satellite (Ref) X-ray emission from northern aurora observed by the Polar Satellite (Ref)

These images were obtained by the NASA Polar Satellite. The X-ray image represents the first global photograph of an aurora in the X-ray spectrum.

Aurora Information and Forecasts

Here is a general discussion of auroras. The Aurora Page has information, links, and images about the northern lights, including links to current sighting reports and aurora forecasts.