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Biology 103
2000 Third Web Report
On Serendip

Aurora Borealis

Katie Gallagher

"The sky is a huge dome of hard material arched over the flat earth. On the outside there is light. In the dome there are a large number of small holes, and trough these holes you can see the light from the outside when it is dark. And trough these holes the spirits of the dead can pass into the heavenly regions. The way to heaven leads over a narrow bridge which spans an enormous abyss. The spirits that were already in heaven light torches to guide the feet of the new arrivals. These torches are called the northern lights."

So believed the Inuit of Hudson Bay (1). Looking up at the night sky, researchers and indigenous people alike have marveled at the bright colorful streaks they called "northern lights." Each had their own theory explaining these strange lights. Some Eskimo stories say that the light was a narrow, dangerous pathway souls traveled to reach heaven, while others believe it to be a collective image of spirits playing football with a walrus skull. Many believed if one whistled toward the light, it would come down and take them away. (2). In Middle-Age Europe, people believed northern lights to be reflections of dead warriors. The warriors who had given their lives for their king and country were honored by being allowed to eternally battle in the skies (1). Early researchers theorized that the lights could be reflected firelight from the edge of the world, sunlight reflected from the ice caps, or perhaps reflected light from ice crystals in the sky (2).

Northern lights, or aurora borealis, are actually caused by solar wind colliding with air molecules in the earth's atmosphere. Solar wind is caused by processes on the surface of the sun. There are three sources of solar wind: interaction between the corona and surface, sunspots, and coronal holes. The atmosphere, or corona, of the sun reaches temperatures of several million degrees Celsius, its surface temperature is approximately 6,000 degrees Celsius, and the interior is also several million degrees Celsius. Because the surface temperature is so much cooler, collisions between gas molecules can cause them to break apart into electrons and nuclei. This resulting gas of free electron and protons, called plasma, escapes through the sun's corona (1). This stream of solar wind blows throughout the solar system at 500-100 km/sec (300-600 mi/sec). It passes by the Earth in about one day (2).

Another source of solar wind is sunspots. A sunspot is a region of concentrated magnetic fields where explosions often occur. Sunspots follow a cycle of 11 years, becoming more intense over time. Although the explosions surrounding them are not well understood, they are known to cause solar wind (2).

Some solar wind also comes from a quiet region of the sun, escaping through coronal holes. A coronal hole is a large region of the sun which is less dense and cooler than the corona around it. This stream of solar wind blows much slower-it takes around 7-10 days to pass by Earth(2, 3).

When the solar wind reaches the Earth, the magnetic fields of the Earth force some of it to compress on the daylight side of the Earth while the rest of it stretches into a tail on the night side of the Earth, resembling a hollow comet, with the top and bottom halves of the tail charged by the opposite charges of Earth's magnetic fields (1).

Solar wind creates a magnetic connection between the Earth and the sun. When it blows across the magnetic fields of the Earth, it can create one million megawatts of electric power, as compared to the few thousand megawatts of power generated by the largest electric power plant. Satellite images show that the aurora is much brighter than all the city lights of North America combined (2).

When the solar wind strengthens, the magnetic tail becomes unstable. Charged particles dive inwards toward the center of the tail, bringing the magnetic fields closer together. The magnetic fields then act as conductors, and when they reach the ionosphere, the energy is converted to light in a process called the quantum leap, resulting in the northern lights that have so fascinated people for ages. When oxygen atoms go through the quantum leap, green light is produced; nitrogen produces red light (1).

Intense auroral displays can also cause serious problems. By increasing the electric currents along electrical conductors, it can cause blackouts in electric power lines and corrosion in oil pipelines, interrupt short wave communication, and even damage electronics and solar panels of satellites to the point of rendering them inoperable. The National Space Weather Program is currently trying to find a way to reduce the damage caused by auroras (2).

Observers claim to hear sound when northern lights appear. The height of the northern lights is 80-130 km above the Earth, in an environment which is almost a vacuum, making it impossible for the sounds to come directly from the auroras. There are several theories regarding this. One theory is that the sound may be coming from discharges in the electrical fields on Earth which occur during an aurora. Another theory is that the electromagnetic energy produced could cause vibrations in certain objects, such as frozen pine needles or loose hair, causing the hissing, swishing or crackling noises heard by spectators. In a laboratory, it was tested that even wearing a pair of glasses could raise one's threshold by 3 or 4 decibels. There is even a theory that the sound is merely a psychological reaction (4).

Like eclipses, many superstitions and myths surrounded the northern lights. Scientists, using technology, have discovered the truth: that the northern lights, termed aurora borealis, are caused by physical and chemical interactions between solar energy and the Earth's own magnetic fields. Although this takes some (but not all) of the mystery out of northern lights, it takes away none of the wonder humans may experience gazing on their beauty.

WWW Sources

1)The Northern Lights, Very informative, a little formal, great pics.

2)The Aurora: Information and Images, Very friendly site - go to Asahi Presents: The Aurora

3)What is a Coronal Hole?,

4)Are Auroral Sounds A Real Physical Effect?, pro-real effect




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