occur around Earth's north and south geomagnetic poles in regions known as
auroral ovals. Southern auroras are called aurora australis; northern
ones, aurora borealis. The aurora is higher in the atmosphere than the
highest jet plane flies. The lowest fringes are at least 60 kilometres
above the Earth, while the uppermost reaches of the aurora extend 900
kilometres above the Earth. The space shuttle flies near 300 kilometres
Although there are stories about the aurora seeming to reach down into the
clouds or to the tops of mountains, these are either illusions or some
phenomenon other than the aurora. Only astronauts can fly through the
Some people believe that the aurora makes sound that accompanies the
ripples and flow of the light. If the aurora does make sound, the sound
would have to be generated here on Earth by some electromagnetic effect.
Any noise generated by the aurora would take a long, long time to travel
all the way to Earth, and the air up by the aurora is much too thin to
carry sound. So does the aurora make noises? Nobody knows for sure!
What causes Auroras?
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. We are protected from the solar wind's
direct effects by Earth's comet-shaped magnetosphere, where the Earth's
magnetic field is distorted by the interplanetary magnetic field and the
solar wind. The electrical energy generated by the charged particles
blowing across the Earth's magnetic field send charged particles down into
the Earth's upper atmosphere.
Nature of Aurora Light
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.
Each atmospheric gas glows with a particular color, depending on its
electrical state (ionized or neutral) and on the energy of the particle
that hits the atmospheric gas. High-altitude oxygen, about 200 miles up,
is the source of the rare, all-red auroras. Oxygen at lower altitudes,
about 60 miles up, produces a brilliant yellow-green, the brightest and
most common auroral color. Ionized nitrogen molecules produce blue light;
neutral nitrogen glows red. The nitrogens create the purplish-red lower
borders and ripple edges of the aurora.
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.
If you have never seen the aurora yourself, videos are available
that will give you some idea of what it is like, but you will have to come
to Alaska in the wintertime to really appreciate the beauty of the aurora.