NORTHERN LIGHTS
Named after the Roman goddess of dawn,”Auroras” occur in both hemispheres. The “Aurora Borealis” (Northern Lights) occur in the northern hemisphere. The “Aurora australis” (Southern Lights) occur in the southern hemisphere. They are almost identical to the Northern Lights and often occur at the same time. More people see “Aurora Borealis” because there are more people living in places where they are visible. [Sources: Kenny Taylor, National Geographic, November 2001; Karen Wright, Discover, July 2000]
The Romans called auroras "blood rain," the Chinese referred to them as "candle dragons," and the Eurasians called them "wind light.” Inuits (Eskimos) believe that auroras reveal the highest level f heaven, where the dead party and dance. In medieval Europe, a red aurora was seen as an omen of an impending bloody battle. Medieval Scandinavians thought the light was a reflection of the sea or scales of massive schools of herring. One man even thought they were generated by lights sucked in by the Greenland ice cap.
Kathy B. Maher of National Geographic wrote: “In Finland the northern lights are called revontulet, or "fox fires," harking back to an old folk tale about an arctic fox running in the snow and touching the mountains with its fur, causing sparks to fly up and illuminate the sky. In another version of the story, the fox throws sparks into the sky by whipping snow upward with its brushlike tail. In northern Lapland, the aurora borealis can be seen more than 200 nights a year, making for some very busy foxes!”
“Auroras” are geomagnetic storms associated with peaks in the sunspot cycles that produce solar wind comprised of billions of tons of plasma and charged particles and can slow satellite orbits, disrupt communication and cause power system to crash. The lights are seen around the magnetic poles of the northern and southern hemispheres. The northern magnetic pole has moved around a triangular area south of the North Pole in the polar islands of northern Canada.
Northern Lights Displays
Auroras most often occur as fuzzy curtains of green light that appear in some parts of the sky. Sometimes, however, they appear as light spectacles with sheets of red, white and green light and even yellow, blue or purple that fill the entire sky.
Spectacular displays include vertical rays that resemble search light beams, star-like coronas made of intersecting rays, draperies made of curving sheets of light that move like a curtain being shaken, and flames of tongue-like rays that ripple upwards. The lights have also appeared as arcs, filaments, patches, spirals and veils that can pulsate, flicker or explode.
Arc-type auroras are the most stable. They can be observed for hours. Auroras can extend for thousands of kilometers and reach 1,000 kilometers into the sky and be linked to a magnetospheric power generator churning out three million megawatts of electricity—or four times the electricity the United States uses during peak summer demand.
Astronauts in the International Space Station look down on the Northern Lights. They say it looks as if the earth is a great dark pond and the aurora is a laser fire. A satellite over Antarctica took spectacular photographs of a green donut of light that surrounded the entire continent.
Descriptions of Northern Lights Displays
Carl Weyprecht, a 19th century Arctic explorer wrote: “The northern lights are an imposing fireworks display—incomprehensible in their scale even for the most vivid imagination. No paint, no brush, and no word can truly describe their glory." In the 1870s, Weyprecht led an Austro-Hungarian expedition to Franz Josef Land, an archipelago in the Arctic Ocean.
One observer wrote: "Streaks of light toss about with abandon. Suddenly, for a second, all light melts away and the sky is full of darkness. Just as quickly the lights blossom again in pulsating waves and arcs, and then, as if to test the credulity of man, giant draperies of it wash by in undulating movements across the whole heavens, sometimes stabbing the ends of their folds towards the earth, dripping with green of grass or red of blood."
Describing the great display in 1989, Kenny Taylor wrote in National Geographic, "The whole dome of the sky was awash with color: cascades of yellow-green and blushes of crimson fanning from a darker point high overhead. As they fell in broad rays, they shifted and changed in brightness, sometimes intense in one places, then cool, then hot. It was like looking up into the heart if a flower of glorious light whose petals rippled in a breeze that could not be felt—a breath from beyond this planet...The show peaked for an hour."
Some people claim they can hear the Northern Lights, www.nationalgeographic.com/ngm/0111 and listen in at www-pv.physics.uiowa.edu/mcgreevy
Where and When to See the Northern Lights
The Northern Lights are usually only seen above 60 degrees latitude. They occur at altitudes of 100 kilometers (60 miles) to 1,000 kilometers (600 miles) above the earth's surface. Typical ones are hundreds of kilometers long but less than a mile wide.
Some of the most intense and frequent Northern Lights displays appears in wide ovals that circle the magnetic the magnetic poles. Spectacular displays are seen around the Hudson Bay because it is near the "enveloped of northern magnetic pole, which is on the northwest tip of Greenland, almost 800 miles from the geographic North Pole. Yellowknife, Canada and Fairbanks Alaska are also popular places to see them. Sometimes a strong solar wing pushed the ovals further south.
The main aurora observation period in the northern hemisphere is from mid-November to mid-April. Although aurora borealis occur anytime of the year, they are most visible in the dark months of winter, when nights are long and days are short. They are also much easier to see when there is no moon and the viewer is far away from city lights. The most spectacular displays usually occur around midnight.
There are often more intense displays in the spring and fall because that is when the earth is most in line with the solar zones with a lot of sunspot and solar flare activity. Summer twilight and full moon light sometimes prevent spectacular auroras from being visible. In some places a hazy green light that lasts from a couple of hours to several days can be seen on many nights. Spectacular displays occur around 25 nights a year.
Solar Wind and the Northern Lights
Auroras occur around the north and south magnetic poles when electrons in the Earth's magnetic field are energized by solar wind and collide with atoms and molecules in thin gases in the earth's upper atmosphere, emitting light.
Solar wind consists of electrically-charged particles and magnetism continually being emitted from the sun. Most of the particles are fast-moving electrons that are projected from the sun at a speed of about 3 million miles per hour and take about 30 hours to cover the 93 million mile distance between the sun and the earth. There is a lesser amount of slow-moving protons.
Large amounts of solar wind is emitted from solar flares. Solar wind is strongest during heightening periods of activity on the sun that often occur in conjunction with large sunspots. Solar storms can disrupt satellites and high-frequency communization, including GPS navigation. Increased drag during these storms can cause satellites to drift off course. Large doses of charged particles can overload a spacecraft’s circuitry.
Magnetosphere and the Northern Lights
The earth's magnetic field forms a protective envelop around the earth’s poles called the magnetosphere, which stretches beyond the moon. Most of particles of the solar wind are deflected by the earths's magnetic fields but some are funneled by the magnetosphere.
When the solar wind arrives in great force it compresses the front end of the magnetosphere and elongates the back into a tail. If the solar wind's magnetic field and the magnetic lines of the earth's magnetic field are properly aligned auroras are formed along the point of impact between the solar wind and the magnetosphere.
The particles of the solar wind are energized and accelerated within magnetosphere and then pulled down toward the earth's surface like a slingshot along the lines of the earth's magnetic field towards the polar regions.
Scientists using information from the IMAGE satellite—a spacecraft designed to observe the earth’s magnetosphere—and a group of four satellites called Cluster—which detect charged particles passing through the magnetosphere—determined that the solar wind pries open large gaps in the earth’s magnetic field, allowing charged particles to penetrate towards the earth. The gaps can stay open for hours at a time, allowing enough particles through to cause geomagnetic storms that can produce 1,000 billion watts of energy, more than the total energy generating capacity of the United States.
What Causes the Northern Lights
When particles of the solar wind reach the tail of the magnetosphere, they break away from the solar wind and reconnect. In a process that is not understood, the reconnecting transforms magnetic energy into kinetic energy.
The kinetic energy propels electrons and positive ions into the earth's atmosphere along the newly reconnected field lines. As these particles, especially the electrons, crash into the atmosphere they collide with atoms and molecules of gases such as oxygen and nitrogen. In each collision the atoms or molecules absorbs energy from the electron then releases it as light.
Scientists still don’t understand a lot the details of the what causes auroras and still can not predict exactly when they occur and what the display will be like. They also do not know why the auroras are more active on some nights than others; how the particle beams receive their energy boost; or why certain shapes and formations are created.
Scientists know that a large amount of solar wind is necessary, and that can be measured with satellites. They also know the magnetic field of particles carried by the solar wind must be aligned opposite the earth's magnetic field, but how all these forces come together is a little like trying to understand how wind, air pressure and water evaporation all come together to make weather.
What Causes the Northern Light Colors
The Color of an aurora depends on the gases involved in the collision and the altitude it takes place. The most specular auroras are produced when the solar wind particles are pulled to the earth with great force, and the light-producing collision are more frequent and intense. The collisions that produce light are not all that different from those that make color and light in neon lights, television screens and computer monitors.
The most common color, pale green is produced by collision with solar wind electrons with oxygen atoms below 250 mile s of latitude. High collision with low-energy electrons sometimes gives off a red glow at the upper edges of the green curtain. Bombarded nitrogen molecules at lower altitude in the ionosphere also give off red light but few solar wind particles have the energy to reach them that is why red is fairly uncommon and occurs most often when there are streams of solar wind. Red auroras are very rare. Perfectly formed ones are said to occur only once in 10 years.
Bombarded charged particles of nitrogen at the top and the ionosphere give off violet or pink light but the light is generally to faint to see. Blue comes from collisions with hydrogen molecules.
Sometimes a green flash appears above the sun as is its sets in Norway. The Green Flash is an unusual second-long green flash of light that occurs sometimes during sunset when the light and the placement of the trees is just right.
Northern Lights, Sunspots and Solar Activity
Auroras are linked with sunspots, which in turn are associated with more intense soalr wind. Sunspots are highly-magnetized areas of the sun's surface. They appear dark because they are slightly cooler than the area around them. Sun spots are usually associated with solar flares (gaseous eruptions with large emissions of electrically charged particles) and prominence (glowing arches of gas that sometimes leap tens of thousands of miles from the sun's surface). Most sunspots appear in certain zones where solar flares explode with high frequency. Some flares reach temperatures in the millions of degrees and release as much energy as tens of millions atomic bomb blasts or volcanic eruptions.
The most brilliant auroras occur about every 11 years when sunspot activity reach it peak. There were brilliant auroras in 1957-58, 1988-89 and 1990-2000. The last period of peak sunspot activity was in 2011-12. On some nights of peak activity scientist counts 200 sun sports. On normal nights the count is as low as two.
It was originally thought that auroras occurred more often during peaks of the 11-year solar cycle. It turns out that assumption is wrong. However really big ones are more likely to occur during peaks of the 11-year solar cycle. During these periods you sometimes get brilliant streaks or red light mixed in with the green.
Famous Northern Lights Displays
An aurora in 1909 was seen at the equator. In 1957 there was a lot of sunspot activity and large elaborate auroras occurred almost every night. On February 9, 1958 a huge eruption occurred on the sun. About a day later a massive amount of solar wind hit the earth's atmosphere and produced a red Aurora that was visible from the Arctic to Cuba. The entire aurora was measured to be 6,000 miles from east to west, 250 miles from north to south, and was from 125 miles to 500 miles above the earth. It was regarded as the largest and most extraordinary aurora of the the 20th century.
On March 13, 1989, another spectacular aurora was produced that was seen as far south as the Yucatan Peninsula, Florida Keys and Arizona. Strong solar wind generated magnetic storms that were so strong they caused satellites to drop several miles from their orbits and produced electrical currents that caused pipelines to corrode. Radio and satellite transmission were lost and coastal navigation systems were disrupted.
During the 1989 solar storm there were reports of garage doors opening and closing on their own, compasses became unreliable, and homing pigeons—which depend on the Earth’s magnetism to find their way—getting lost. Quebec was close to the "eye" of some of the storm. In March 1989 it experienced a complete power blackout that shut down elevators in mid flight, stopped subways in Montreal during rush hour, and blackened homes for nine hours. The radiation levels were not enough to harm people on the ground but they were strong enough to give people flying in airplanes radiation equivalent to one chest X-ray.
There were spectacular northern light displays in the fall of 2003. Solar storms associated with a large sunspot produced a solar wind and auroras that were seen as far south as the Florida panhandle. There was also vivid displays in January 2004 and September 2005.
Northern Lights Research
Poker Flat Research Range (30 miles northeast of Fairbanks, Alaska) is one of the main centers of aurora research. An Alaskan researcher has tried prove there is a link between the northern lights and homicide and accidental death rates.
The study of Auroras includes firing rockets into auroras and measuring the energy emitted from electrons and ions. Artificial auroras have been made with barium ions and other chemicals and radiation released hundred of miles above the earth surface with rockets.
Spacecraft have observed the convergence zone of the magnetic field of the sun and the earth and waves of energy flowing along the magnetic field lines at more than 6,000 miles a second.
Image Sources:
Text Sources: New York Times, Washington Post, Los Angeles Times, Times of London, Lonely Planet Guides, Library of Congress, U.S. government, Compton’s Encyclopedia, The Guardian, National Geographic, Smithsonian magazine, The New Yorker, Time, Newsweek, Reuters, AP, AFP, Wall Street Journal, The Atlantic Monthly, The Economist, Foreign Policy, Wikipedia, BBC, CNN, and various books, websites and other publications.
Last updated May 2016