mythology the Valkyries (immortal, war-like virgins) would come
galloping across the night sky upon their horses equipped with
helmets, spears and armor that would glow and shimmer in the
darkness. These lights, colored red, blue, violet and green,
would spread in curtains from horizon to horizon, amazing the
is how the Vikings explained a phenomenon we now call the aurora
borealis, or the Northern Lights. The lights are usually
visible in the sky from the northern latitudes though under
unusual conditions they can be seen as far south as Florida
and Mexico. A similar phenomenon known as the aurora australis
(or the Southern Lights) can be appreciated from the southern
latitudes. Historically these have been less easily observed
by people, however, because of the smaller land mass and lower
populations in the area of the South pole when compared to the
Between 600 (969km) and 60 miles (96km) in altitude
Mostly green, with red, pink, blue and violet.
Aurora comes from the Roman God of dawn and Boreas
is the Greek word for the north wind
Kristian Birkeland developed the first correct theory
of the phenomenon in 1908.
The aurora borealis is visible in the northern latitudes
and its counterpart, aurora australis, is visible in Earth's
By: Electrons from the solar wind follow magnetic
field lines to the poles where they excite gases in the
atmosphere to glow
Strong solar flares can cause a geomagnetic storm
which causes the lights to be seen much further south than
name of the effect itself comes from the Roman god of the dawn,
Aurora, and the Greek name for the north wind, Boreas. The French
scientist Pierre Gassendi is generally credited for coming up
with the title in 1621; however, written observations of the
effect stretch back as far as 2600 B.C in China.: Fu-Pao,
the mother of the Yellow Empire Shuan-Yuan, saw strong lightning
moving around the star Su, which belongs to the constellation
of Bei-Dou, and the light illuminated the whole area.
societies have explained the phenomenon in diverse ways. The
Alaskan Inuits thought of the lights as the souls of deer, seals,
salmon and whales that they hunted. The Menominee Indians in
North America thought the glow must be the torches of giants
that lived in the North. In the Middle Ages the Europeans assumed
that when the shimmering signs appeared in the sky they must
be a message from God. Many groups thought of the lights as
clashing armies in the heavens, perhaps a warning of an impending
disaster. In 1862 the aurora borealis made a rare appearance
in the skies of Virginia during the Battle of Fredericksburg,
a sign that the Rebel forces took to mean that God was on their
Birkeland conducted a series of experiments in the early
20th century that helped establish the mechanism behind
the aurora borealis.
times brought scientific explanations. In the late 1700's Benjamin
Franklin observed the Northern Lights during his trips across
the Atlantic to Europe and theorized that they were caused by
a concentration of electrical charges in the polar regions intensified
by the snow and other moisture. He thought that as the area
became overcharged there must be a release of power into the
air causing the illumination. Franklin was right about the phenomenon
involving electricity, but it wasn't untill Kristian Birkeland,
a Norwegian scientist, did a series of experiments in the early
20th century that a full theory of effect was developed. Birkeland
thought that electrons coming from the sun were guided to Earth's
poles through the planet's magnetic field. There they interacted
with the Earth's atmosphere to cause the lights.
know that in the corona (or upper atmosphere) of the sun, temperatures
can reach over a million degrees. This is so hot that atoms
break down into their component parts: electrically-charged
electrons and protons. Some of them are launched out from the
sun at up to 500 miles per second in a phenomenon known as the
"solar wind." After about three days these charged particles
reach the earth.
below a curtain can appear as a series of rays.
solar wind would be dangerous to life on our planet, but fortunately
our the earth possesses a magnetic field generated by the rotation
of planet's iron core. This field, called the magnetosphere,
directs most of the charged particles around the globe. A small
portion of the particles, however, are trapped in the field
and follow it down to the earth's magnetic North and South Poles.
The electrons remain invisible to our eyes until they collide
with gas molecules in the upper atmosphere. When an electron
is absorbed by an atom, the atom becomes ionized, or excited.
The atom then loses that excitement by emitting a photon of
light or by colliding with another atom or molecule. The color
of the emitted photons depends on which gas molecule is struck
and at what altitude. At heights of 250 miles (402km) or above,
oxygen will glow green and below that point, red or pink. A
nitrogen molecule hit from 80 to 100 miles (80 to 160km) up
produces blue or violet. Between 60 and 80 miles(96 to 128km)
in altitude both nitrogen and oxygen glow pink.
are not limited to Earth, but have been seen on Jupiter, Saturn,
Uranus and Neptune along with some of their moons. Venus also
has an Aurora effect, but because the planet has no magnetic
field, the lights are distributed in patches across the entire
planet, not just around the poles.
aurora in the upper atmosphere as seen from the International
shape of the aurora glow in Earth's sky depends on the shape
of the magnetic field lines and the location of the observer.
They are most often seen as curtains that tend to run east to
west. If the observer is farther south than the aurora it will
appear near the horizon, if he is directly beneath it, it will
be seen overhead. Lights that are located directly above often
appear more as rays than curtains because of the perspective
of the viewer. The shape of the aurora can be static for many
hours or change rapidly. Their brightness varies from a barely
visible glow to giving enough illumination so that it is possible
to read a newspaper at midnight. The lights are never bright
enough, however, to be seen when the sun is up.
the effect is limited to the auroral zone, which is typically
10° to 20° from Earth's magnetic poles. However, powerful solar
flares can cause an increase in the solar wind setting off a
geomagnetic storm. The incoming wind can compress the magnetosphere
of the earth, allowing charged particles to come closer to the
planet than they normally would. This can cause serious damage
to satellites in high orbit. The storm can also force many more
charged particles to stream into the Earth's atmosphere at lower
latitudes than normal. This has been known to cause power outages
on the ground. Under these extreme conditions it is possible
to observe the aurora borealis much further south than usual.
of 1859 a gigantic solar flare caused perhaps the most spectacular
Northern Lights display in recorded history. New York Times
reported that even as far south as Boston that the aurora was
"so brilliant that at about one o'clock AM ordinary print could
be read by the light". The connection between this solar flare
and the increase in the aurora borealis was so obvious that
it helped scientists firmly establish a link between the two
and sent them down the right path to finally explain this wonderful,
but mysterious phenomenon of nature.
2012 Lee Krystek. All Rights Reserved.