Реферат: Aurora Borealis 2 Essay Research Paper INTRODUCTIONOne
Aurora Borealis 2 Essay, Research Paper
One of nature=s most spectacular phenomenons to date is the once mysterious aurora. This dazzling show of lights has been working its magic for people around the world for several years. But, few know the cause of this amazing light display. It is the purpose of this report to reveal this mysteryC a mystery that scientists aspired to solve for nearly 300 years.
WHAT IS AN AURORA?
An aurora is a luminous atmospheric phenomenon that can be seen most frequently above 60. North or South latitude, and sometimes spills over to other parts of the world. It consists of rapidly shifting patches and dancing columns of light of various colours. Dramatic displays occur around spring and fall equinoxes but the aurora can be seen any cloudless night, the best time being around midnight in the winter. It is named according to its location, Aurora Borealis meaning the northern lights, and Aurora Australis meaning the southern lights. The general name for both is Aurora PolarisC since both displays occur at the earth=s poles.
WHAT CAUSES AN AURORA?
For many years, the ideas about what causes an aurora were left to old legends and unsubstantiated theories. The inuit believed that the northern lights were the spirits of dead relatives, dancing around in the sky, while the Vikings believed that they were caused by a fire on the edge of the world. In the fourteenth century, Aristotle described the auroras as jumping goats caused by the earth=s vapours being set on fire by meteors. Later on, in 1707, a Norwegian physicist claimed that they were caused by steam and smoke that escaped from a heat source beneath Greenland. It was not until the late 1950’s that scientists finally discovered the true cause of the aurorasC Solar Wind.
Approximately every eleven years, explosions erupt from sun spots creating what are called Solar Flares. These flares can extend tens of thousands of kilometres high and reach temperatures of 20 million degrees Celcius. They also propel Solar Wind, which is a stream of radiation and plasmaC a spray of charged particles. This solar wind, which can travel through space at 1-3 million km/h, approaches and threatens earth two to three days after leaving the sun. At approximately 65,000 km from the earth=s surface, the wind encounters=s the earth=s magnetic field. Most of it is deflected by the field while some leaks in where the magnetic field lines enter the earthC the earth=s magnetic poles. Since the solar wind carries the sun=s magnetism with it, the portion that leaks in reacts with the earth=s magnetic field lines, producing electric power. This newly produced stream of electrons, now named Birkland=s Currents, follows the earth=s field lines into the north and south poles.
When 10,000 km above ground, the Birkland=s Currents begin to shape like curtains and begin to accelerate. At about 100-200 km from ground, they run into the Oxygen and Nitrogen gases in our atmosphere. When hit by this stream of electrons, the O2 and N2 molecules become excited and emit light. This is what we see as an aurora.
A Germanic Norse legend attempted to explain the colours of the auroras by attributing them to the colourful dresses of princesses that danced in the sky. This is obviously not the case. In fact, the gases of our atmosphere, the O2 and N2, are responsible for the colours seen in auroral displays.
When the electrons of a gas molecule are excited, they begin to jump energy levels, releasing energy in the form of light. The colour of the light depends on the molecule, as each different gas emits its own characteristic colour. In the case of auroral gases, the Oxygen emits a yellow-green light while the Nitrogen emits a violet-red light.
The order in which the auroral colours appear to us is also due to the gases. As the aurora comes closer and closer to earth, the air becomes thicker and the excited gas molecules begin to lose their energy to surrounding air molecules, thus producing less light. The Nitrogen, which has the better ability to glow in thicker air, is seen on the lower end of the auroraC the end nearest to the groundC while the Oxygen gas, which glows best in thinner air, is seen at the top of the aurora.
Many Inuit, as well as other credible sources, have reported hearing a Aswishing@ sound accompanying an outburst of auroral light. But, auroras are not logically expected to make a sound since they are not associated with any sound waves that we can hear. And even if a sound existed, it would take at least five minutes to reach earth which does not support the claims that the sound accompanied a quick outburst. A possible explanation for these Aswishing@ sounds could be the build up of static during an auroral display. Another possibility concerns a certain type of crystal found in soil and rocks. Radiowaves produced during auroras may reach earth and react with these crystals, causing them to expand or contract. People with sensitive hearing may be able to pick the noises accompanying this process.
It is difficult to believe that the mystery of the auroras took 300 long years to solve. But, it is true. Although many physicists came close throughout the years, it took until the 1950’s to develop the necessary equipment to determine the cause of these magnificent luminous displays. While studies about what goes on in an aurora are ongoing, people around the world continue to enjoy both the northern and southern lights. Regardless of what causes them, they represent one of the most beautiful natural phenomenons of this world, and will continue to do so for years to come.