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Question:

    What are the northern lights?

Answer:    

    The northern lights, one of several astronomical phenomena called polar lights (aurora polaris), are shafts or curtains of colored light visible on occasion in the night sky.

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:

  • According to Neil Bone (The aurora: sun-earth interactions, 1996), the term aurora borealis--northern dawn--is jointly credited to have first been used by Pierre Gassendi (1592-1655) and Galileo Galilei (1564-1642), who both witnessed a light display on Sept. 12, 1621. However, Bone also includes a description of the northern lights made 1,000 years prior by Gregory of Tours (538-594.) It included the phrase, "... so bright that you might have thought that day was about to 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.
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Library of Congress Web SiteFurther 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.

SearchFor more print resources...
Search on "Auroras," or "Aurora borealis," in the Library of Congress Online Catalog.

Photo:  white swirls of light in a dark blue sky, trees and show in the foreground.
Gates of the Arctic National Park and Preserve Student Handbook, National Park Service Web site.

Drawing of the earth surrounded by lines representing the  magnetic fields.
A simplified depiction of solar winds and their effect on the Earth's magnetic field. Dr. Nicholas Short's Remote Sensing Tutorial, NASA.

Sktech of Van Allen belts with  red  lines radiating out from them.  The lines   are more compressed on the left side than the right.
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.

Photo:  A vertical streak of yellow and white light next to a patch of pierces a dark green sky,  Photo:  A vertical streak of yellow and white light pierces a dark green sky over the silhouettes of pine trees.  A deep red patch of light is just to the left of the yellow-white streak.
Skywatcher Chart - Aurora Borealis, National Weather Service, NOAA.

Reds, yellows and greens light up the sky  over some houses.
This photo of an Aurora Borealis display was taken on November 5th, 2001 in Rapid City SD.

Streaks of purple, blue and teal on a black background.
View of the Aurora Borealis from the Space Shuttle. Dr. Nicholas Short's Remote Sensing Tutorial, NASA.

Black and white photo of a cloud of light over a settlement.
The aurora borealis as seen at Dawson, the capitol of Yukon Territory, c1908. Prints & Photographs Division, Library of Congress.

Black and white print depicting  northern lights over a wooden fort.
Northern Lights over fort at Sitka, Alaska. Prints& Photographs Division, Library of Congress.

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  October 25, 2013
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