Polar lights (aurora polaris) are a natural phenomenon
found in both the northern and southern hemispheres that can be
truly awe inspiring. Northern lights are also called by their scientific
name, aurora borealis, and southern lights are called aurora
australis.
Sten Odenwald, author of The 23rd cycle, learning to live
with a stormy star (New York, Columbia University Press, c2001), provides
insight to how northern lights are formed:
The origin of the aurora begins on the surface of
the sun when solar activity ejects a cloud of gas. Scientists call
this a coronal
mass ejection (CME). If one of these reaches earth, taking about
2 to 3 days, it collides with the Earth’s magnetic field.
This field is invisible, and if you could see its shape, it would
make
Earth look like a comet with a long magnetic ‘tail’ stretching
a million miles behind Earth in the opposite direction of the sun.
When a coronal mass ejection collides with the magnetic field,
it causes complex changes to happen to the magnetic tail region.
These changes generate currents of charged particles, which then
flow along lines of magnetic force into the Polar Regions. These
particles are boosted in energy in Earth’s upper atmosphere,
and when they collide with oxygen and nitrogen atoms, they produce
dazzling auroral light.
Odenwald further tells us "Aurora are beautiful, but the
invisible flows of particles and magnetism that go on at the same
time can damage our electrical power grid and satellites operating
in space. This is why scientists are so keen to understand the
physics of aurora and solar storms, so we can predict when our
technologies may be affected."
Can I see them anywhere?
Yes. Although more frequent at higher latitudes, closer to the
poles (such as in Canada, Alaska, Antarctica), they have been
seen closer to the equator as far south as Mexico. To view them,
look in the direction of the closest pole (the northern horizon
in the northern hemisphere, the southern horizon in the southern
hemisphere).
Can I see them at any time of the year?
Yes. In some areas, such as Alaska or Greenland, they may be visible
most nights of the year. And they occur at any time of the day,
but we can’t see them with the naked eye unless it’s
dark.
What causes the colors and patterns?
Colors and patterns are from the types of ions or atoms being energized
as they collide with the atmosphere and are affected by lines
of magnetic force. Displays may take many forms, including rippling
curtains, pulsating globs, traveling pulses, or steady glows.
Altitude affects the colors. Blue violet/reds occur below 60
miles (100 km), with bright green strongest between 60-150 miles
(100-240 km). Above 150 miles (240 km) ruby reds appear.
Fun Facts about northern lights:
- The name “Aurora Borealis” is credited to Galileo
Galilei (1616) and means “northern dawn.”
- Auroras have been observed since ancient times.
- The height of the displays can occur up to 1000 km (620 miles),
although most are between 80-120 km.
- Auroras tend to be more frequent and spectacular during high
solar sunspot activity, which cycles over approximately eleven
years.
- Some displays are particularly spectacular and widespread and
have been highlighted in news accounts. Examples include auroral
storms of August-September, 1859, Feb 11, 1958, (lights 1250
miles wide circled the Arctic from Oregon to New Hampshire) and
March 13, 1989, (the whole sky turned a vivid red and the aurora
was seen in Europe and North America as far south as Cuba).
- Legends abound in northern cultures to explain the northern
lights. Some North American Inuit call the aurora aqsarniit (“football
players”) and say the spirits of the dead are playing football
with the head of a walrus. Often legends warn children that the
lights might come down and snatch them away.
- June 1896, Norwegian Kristian Birkeland, the “father
of modern auroral science,” suggested the theory that electrons
from sunspots triggered auroras.
- Yellowknife (Northwest Territories, Canada) is the capital
for aurora tourism.
- The earliest known account of northern lights appears to be
from a Babylonian clay tablet from observations made by the official
astronomers of King Nebuchadnezzar II, 568/567 BC.
- Some people claim to hear noises associated with the northern
lights, but documenting this phenomenon has been difficult.
 Related
Web Sites |
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 Further
Reading |
- Berry,
Janice. Aurora borealis: a photo memory. Anchorage,
AK, Todd Communications, c1999. 64 p.
- Bone,
Neil. The aurora: sun-earth interactions. 2nd
ed. Chichester, NY, Wiley, 1996. 172 p.
- Brekke,
Asgeir, and Alv Egeland. The northern lights: their
heritage and science. Translated by James Anderson.
Oslo, Grøndahl Dreyer, c1994. 168 p.
- Cowen,
Robert C. How northern lights affect your local power
and light. Christian science monitor, v. 88,
May 29, 1996: 3.
- Davis,
T. Neil. The aurora watcher’s handbook. Fairbanks,
University of Alaska Press, 1992. 230 p.
- Eather,
Robert H. Majestic lights, the aurora in science,
history, and the arts. Washington, American Geophysical
Union, c1980. 323 p.
- Falck-Ytter,
Harald. Aurora: the northern lights in mythology,
history, and science. Translated by Robin Alexander.
Edinburgh, Floris, 1999. 143 p.
- Green,
James L., and others. Eyewitness reports of the great
auroral storm of 1859. Advances in space research,
v. 38, no. 2, 2006: 145-154.
- Harrison,
Giles. Aurora diaries. Astronomy & geophysics, v.
46, Aug. 2005: 4.31-4.34.
- Jago,
Lucy. The northern lights; the true story of the
man who unlocked the secrets of the aurora borealis. New
York, Knopf, 2001. 297 p.
- Kalz,
Jill. Northern lights. Mankato, MN, Creative
Education, 2004. 32 p. (Juvenile literature)
- Kelley,
David H., and Eugene F. Milone. Exploring ancient
skies: an encyclopedic survey of archaeoastronomy. New
York, Springer, c2005. 612 p.
- Silverman,
S. M. Comparison of the aurora of September 1/2, 1859
with other great auroras. Advances in space research,
v. 38, no. 2, 2006: 136-144.
- Odenwald,
Sten. The 23rd cycle: learning to live with a stormy
star. New York, Columbia University Press, c2001. 207
p.
- Souza,
D. M. Northern lights. Minneapolis, Carolrhoda
Books, c1994. 48 p. (Juvenile literature)
- Stephenson,
F. Richard, David M. Willis, and Thomas J. Hallinan.
The earliest datable observation of the aurora borealis. Astronomy & geophysics,
v. 45, Dec. 2004: 6.15-6.17.
- Taylor,
Kenny. Auroras: Earth's grand show of lights. National
geographic, v. 200, Nov. 2001: 48-63.
- Wright,
Karen. Seeing the light. Discover, v. 21, July
2000: 50-56.
|
 For
more print resources...
Search on "Auroras," or "Aurora
borealis,"
in the Library of Congress Online
Catalog.
|
Gates
of the Arctic National Park and Preserve Student Handbook,
National Park Service Web site.
A simplified
depiction of solar winds and their effect on the Earth's magnetic
field. Dr. Nicholas Short's Remote Sensing Tutorial, NASA.
A cutaway
sketch of the doughnut-shaped Inner and Outer Van Allen Belts.
The lines are streamlines representing solar wind particles as
they passed through Earth's magnetic field. Dr. Nicholas Short's
Remote Sensing Tutorial, NASA.
Skywatcher
Chart - Aurora Borealis, National Weather Service, NOAA.
This photo
of an Aurora Borealis display was taken on November 5th, 2001 in
Rapid City SD.
View of the
Aurora Borealis from the Space Shuttle. Dr. Nicholas Short's
Remote Sensing Tutorial, NASA.
The
aurora borealis
as seen at Dawson,
the capitol of
Yukon Territory,
c1908. Prints & Photographs
Division, Library
of Congress.
Northern
Lights over fort
at Sitka, Alaska. Prints& Photographs
Division, Library
of Congress.
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