Lessons >>> Lesson 24
To a person seeing the Aurora Borealis or "northern lights" for the first time, it is an uncanny awe-inspiring spectacle. Sometimes it begins as a glow of red on the northern horizon, ominously suggesting a great fire, gradually changing to a curtain of violet-white, or greenish-yellow light extending from east to west. Sometimes this may be transformed to appear as fold upon fold of luminous draperies that march majestically across the sky; sometimes as a vast multitude of gigantic flaming swords furiously slashing at the heavens; sometimes as a flowing crown with long undulating colored streamers fanning downward and outward.
The Northern lights have been described in ancient times by the Eskimos, American Indians, polar explorers and even mentioned in the Old Testament.
On some occasions, when the Aurora reached the middle latitudes of France and Italy, it struck fear into the population. When they reached these latitudes, they were a dark red in color and thought of as an omen of disaster and outbreak of a war. More recently, the northern lights were taken as omens of war when they were visible from London during Germany's 1939 blitzkrieg, and on December 7, 1941, when they were seen as far south as Cleveland, Ohio, on the day that Japan attacked Pearl Harbor.
The ancient people were awed by the Aurora. Folklore abounds with explanations of the origins of the spellbinding celestial lights. Every Northern culture has legends about the lights and often associates them with life after death. Various cultures have explained the Aurora Borealis as dancing spirits or blood raining from the clouds. Some believed they were caused as a result of fungi on rotting wood, others believed they were magic, while many believed they were in the presence of temperamental gods and summoning spirits. Aurora was the Roman goddess of the dawn. Boreal is a Latin word, meaning "north." Thus, the northern lights. In the Antarctic, the lights are called the Aurora Australis, or southern lights.
The Finnish name for the lights (revontulet) comes from a Sami, or Lapp, legend whereby the tail of a fox running along snow-covered fells strikes the snow drifts, sending a trail of sparks into the sky. Revontulet literally means "foxfire". The Vikings believed the aurora was the beautiful maidens called Valkyries, which escorted those killed in battle to the gods. The Sami people of Lapland believed they had power over the lights, and whistling under them would cause them to come closer. The Inuit of Alaska believed that the lights were the spirits of the animals they hunted: the seals, salmon, deer and beluga whales. Many ancient peoples would not stare at or speak of the aurora, due to a fear of insulting their divine nature.
The East Greenland Eskimos believed the Aurora is the spirits of children who died at birth. The Point Barrow Eskimos considered the Aurora an evil thing. In the past they carried knives to defend themselves from the lights. Most Eskimo groups have a myth of the northern lights as the spirits of the dead playing ball with a walrus head or skull. The Eskimos of Nunivak Island had the opposite idea, of walrus spirits playing with a human skull.
However enchanting and intriguing explanations of the indigenous people were, we didn't actually begin to find the real rationalization for the Northern Lights until 1774, when Jean Jacque Dortous de Mairan of France linked the auroras to solar activity.
The origin of the Aurora is 93 million miles (149 million km) from Earth at the Sun. The sun gives off high-energy charged particles (electrons and positive ions) that travel out into space at speeds of 200 to 440 miles per second. A "cloud" or gas of such ions and electrons is called plasma. The stream of plasma coming from the sun is known as the solar wind. As the solar wind interacts with the fringes of the earth's magnetic field, the particles are "shocked" into flowing around the earth.
Most of the energetic particles from the Sun are deflected around the Earth by the magnetosphere, but some get trapped. Electrons trapped in the Earth's magnetic field (the magnetic mirror effect) are accelerated along the magnetic field toward the Polar Regions and then strike the gases into the upper layer of the atmosphere, called the ionosphere.
In the ionosphere, the speeding electrons collide violently with gas atoms. This gives the gas atoms energy, which causes them to release both light and more electrons. In this way, the gases of the ionosphere start to glow producing the spectacle that we know as the auroras, northern and southern.
Variations in colour are due to the type of gas particles that are colliding. The most common auroral color, a pale yellowish-green, is produced by oxygen molecules located about 60 miles above the earth. Rare, all-red auroras are produced by high-altitude oxygen, at heights of up to 200 miles. Nitrogen produces blue or purplish-red aurora.
In addition, auroras are not only fascinating to watch because of their varying colors, but also because of the many shapes that can be manifested. The shape completely depends on the fluctuations of the earth's magnetic field. A combination of the auroral arc and drapery or curtain type is one of the finest displays that can be seen. Collections of curtains evolve into soft billowy clouds which can brighten and fade in a matter of seconds. During some exceedingly bright displays, the aurora's shimmering glow has been reported to be as bright as the full moon. These fine displays occur at an altitude of from 65-70 miles, while the lower limit is 40 miles and the upper limit is 600 miles.
The location of auroras on Earth is strongly controlled by the Earth's magnetism. The auroras appear most frequently over the Earth's polar regions in what are known as the auroral ovals; in the northern hemisphere the auroral oval bulges that much further to the south, the stronger the solar wind is at any given moment. The oval normally extends over northern Finland and Scandinavia, the whole of Canada and the northern USA, Alaska and Siberia.
Auroras are most intense at times of intense magnetic storms caused by sunspot activity. Magnetic storms expand the auroral zone to locations more distant from the magnetic pole - such as Washington, London or Beijing - and also create bright auroras. If this happens on a clear night, residents in those cities can see an aurora, but it is a rare treat for them.
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