The Aurora has a curtain-like shape, and the altitude of its lower edge can be sixty or seventy miles high. This is about ten times higher than a jet flies.
The auroral zones, in which maximum activity is seen by observers on Earth, are located in latitudes 67 degrees north and south, and are about 6 degrees wide.
Auroras Occur along ring-shaped regions around the north and south geomagnetic poles. Fairbanks, Alaska, is a good place for aurora watching because it is under this auroral zone in the north. Aurora are seen on all gas planets in our solar system. Auroras on planets besides the Earth are only red because the atmosphere's contain only hydrogen and not oxygen.
Like a neon sign, auroral light is produced by a high-vacuum electrical discharge. It is powered by interactions between the Sun and earth. The light is the glow from atoms and molecules in the earth's upper atmosphere.
In the north hemisphere auroras are called aurora borealis, or northern lights; in the southern hemisphere the aurora is called the aurora australis.
The Sun is a ball of gases that is so hot its outermost part blows away as solar wind. This wind is made up of charged particles. These particles travel to earth in about two days. These gases are what give the aurora it's color.
The upper atmosphere contains, at the lower edge of the aurora, a thin and partly ionized layer called the ionosphere. Reflected by the ionosphere, radio waves can propagate great distances by bouncing between it and the ground.
Auroral displays indicate that the ionosphere and our protective atmosphere are being energized by the electric power generated in the magnetosphere. As these electrical currents are discharged in the ionosphere, many phenomena are produced, including the visible emissions we recognize as the aurora and magnetic storms.
Auroras are similar to color television images. In the picture tube, a beam of electrons controlled by electric and magnetic fields strike the screen, making it glow in colors that vary with the screen's phosphorous. Auroral color depends on the type of atoms and molecules struck by the energetic particles, particularly electrons, that rain down along earth's magnetic field lines in the discharge process. Each atmospheric gas glows with a specific color, depending on whether it is ionized or neutral, and on the energy of the particle hitting the atoms and air molecules
The brightest and most common auroral color, a brilliant yellow-green, is produced by oxygen atoms at an altitude of roughly 60 miles. High-altitude oxygen atoms (about 200 miles) produce rare, all red auroras. Ionized nitrogen molecules produce blue light; neutral nitrogen molecules create purplish-red lower borders and ripple edges.
The magnetosphere protects us from the direct effects of the solar wind, but auroras can disrupt radio communications, some defense-related radar systems, and power transmission lines. Currents created by changing magnetic fields accompanying aurora even cause corrosion in pipes. This corrosion potential was taken into account during the design and building of the Trans-Alaska pipeline.
©Copyright 1998 Elizabeth
Beckett, Holly Bernitt, and Vishwa Chandra.