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Danish Polar Center Danish Agency for Science, Technology and Innovation
page 12 of 60
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Aurora borealis northern lights
The aurora borealis (northern lights), and the aurora australis (southern lights) are beautiful, dynamic,
luminous displays seen in the night sky in the northern and southern latitudes, near the poles.
The aurora is a very large-scale phenomenon encircling the entire polar regions, but when one views a
particular display from the ground only a very small portion is visible. Most aurora have basically a curtainlike
or ribbon-like form. As the auroral activity increases, folds develop, the complexity and extent of the
folds depending on the degree of activity.
Though the aurora appears to come near to the ground, the light originates high in the atmosphere. The
lowest aurora are about 100 km above the ground, with the highest extending to 400 km. This is much
higher than clouds or the highest flying aircraft.
The Sun is a stormy place and has its own weather. It is so hot and dynamic that it cannot keep its
atmosphere contained by its gravity. Instead, energy flows out from the Sun toward the Earth in a stream of
electrified particles. Moving at a 1,600,000 km/hr, this hot, ionized gas - called plasma - carries particles
and magnetic fields from the Sun outward past the planets.
This stream of charged particles is called the solar wind. The solar wind is constantly streaming toward
Earth from the Sun. When the Sun is more active, observed as sunspots and other changes, the solar wind
blows harder.
The Earth is shielded from the full blast of these particles by its magnetosphere, a large bubble of magnetic
field that deflects the solar wind. Some of the charged particles in the solar wind are captured by the Earth's
magnetic field and speeded up as they travel down magnetic field lines toward the auroral ovals.
These particles gain energy so that when they blast into the atmosphere they cause the air to glow. When
these high energy particles collide with oxygen and nitrogen in Earth's atmosphere, some of the energy is
turned into light, the aurora.
Danish Polar Center
IPY Service Manual for Kangerlussuaq 2008
version 1 June 2008
Compiled and written by Henning Thing (het@fi.dk)
Danish Polar Center Danish Agency for Science, Technology and Innovation
page 13 of 60
Auroral light is similar to light from a colour television set. In the picture tube, a beam of electrons strikes the
screen, making it glow in different colours, depending on the type of chemicals that coat the picture tube.
The chemicals are called phosphors and glow red, green or blue.
Auroral light is from the air glowing as high-energy electrons stream down Earth's magnetic field lines and
collide with molecules in the atmosphere. Each gas in the atmosphere glows with a particular colour,
depending on whether it is neutral or charged, and on the energy of the particle that hits it.
Diagram from University of Alaska Geophysical Institute
http://vathena.arc.nasa.gov/curric/space/aurora/aurofaq3.html
Atomic oxygen, about 100 km up, is the source of the greenish-white light common in aurora displays. High
altitude atomic oxygen, about 320 km up, can also emit a dark red light under some circumstances resulting
in the "bloody red" auroras produced during great magnetic storms.
Nitrogen molecules, lower in the atmosphere, produce a red light when they are struck by electrons. This is
the faint red that is often seen along the bottom edge of a aurora curtain. High in the atmosphere nitrogen
molecules can become ionized and emit blues and violets.
In the upper atmosphere accelerated electrons blast into oxygen and nitrogen atoms and molecules and
give them energy. This energy is absorbed causing a "quantum leap" in the electrons of the atom or
molecule. This "excited" atom cannot keep this energy for long and releases the energy as a small burst of
light, called a photon, of a particular wavelength. The wavelength determines the colour or the light. Now
the atom or molecule is back to its unexcited state, having given off its energy in the form of light. Billions of
atoms and molecules undergoing these electron excitations are what produce the light in the aurora. The
colour of the light is determined by the particular "quantum" of energy absorbed and released by the atom
or molecule.
Neon lights produce light in the same way. The neon atoms in the gas discharge tubes get energized by the
electricity passing through the tube. The atoms become excited and their electrons make "quantum leaps"
to outer regions in the atom. When the electrons lose this energy they give off a small burst of light, called a
　
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