Aurora Information
Compiled by the
Public Information and Education Outreach Office

Aurora Borealis, the Northern Lights, are dynamic, colorful displays of light that occur continuously along ring-shaped regions around the north and south geomagnetic poles. These rings are fueled by an electrically charged wind that blows through the solar system and is pulled close to the earth by magnetic fields around the poles.

Auroras hang like curtains in the sky above Fairbanks, Alaska, which lies directly under the auroral ring. The lower edge of the auroral curtain is sixty or seventy miles above Earth, which is about ten times higher than a jet aircraft flies. Mirror images of each display in the north occur over the south pole as the Aurora Australis. Like a neon sign, auroral light is produced by a high-vacuum electrical discharge. The sun, a hot ball of gases, continuously blows away its outermost edges, creating a solar wind. Consisting of charged particles, this tenuous gas travels to Earth in about three days. Because Earth's magnetic field prevents the solar wind from penetrating our atmosphere, its solar particles stream around our planet, encasing Earth and its magnetic field within a comet-shaped cavity called the magnetosphere.

The solar wind interacts with the magnetosphere, causing it to behave as a generator that produces up to ten million megawatts of electrical power.

The magnetosphere protects us from the direct effects of the solar wind, but currents created by changing magnetic fields accompanying the aurora can seriously disrupt radio communications, radio navigation, some defense-related radar systems, and power transmission lines. They also can cause corrosion in pipes, including the trans-Alaska pipeline.

Auroras are similar to color television images. In the picture tube, a beam of electrons controlled by electric and magnetic fields strikes the screen, making it glow in a variety of colors.

Auroral color depends on the type of atoms and molecules struck by the energetic particles that rain down along Earth's magnetic field lines in the discharge process. Each atmospheric gas glows with a specific color.

The brightest and most common auroral color, a brilliant green-yellow, is produced by oxygen atoms at roughly 60 miles altitude. High-altitude oxygen atoms (about 200 miles above Earth) produce rare, all-red auroras. Ionized nitrogen molecules produce blue light; neutral nitrogen molecules create purplish-red lower borders and ripple edges.

Auroral intensity varies with levels of solar activity, which seem to follow an 11-year cycle. That cycle is characterized by erratic bursts of solar flares at the high end of the cycle and relatively stable solar activity at the low end. A few years after a maximum year of solar activity, auroras in high latitudes are brilliant.

Auroras can be seen frequently on clear winter nights in Alaska from late evening through the early morning hours. Intense auroras can be seen in the continental U.S., particularly in the north, when solar activity is high.