Tuesday, September 12, 2006

Aurora Borealis/Australis/Polaris

~~ This is one of my favorite phenomenoms as it is the most beautiful and ethereal... Lots of good stuff here, so read on!!

The name

The northern lights have had a number of names through history. The scientific name for the phenomena is Aurora Borealis, which is Latin and translates into the red dawn of the north. It was the Italian scientist Galileo Galilei (1564-1642) who first used the expression. On the latitude where Galileo was living, northern lights consist of mainly red colour.
In this web site we will use the terms northern lights, aurora, aurora borealis and polar lights to describe it.
Aurora Borealis - Northern Lights - Nordlys(Norwegian)
Aurora Australis - Southern Lights - Sørlys(Norwegian)
Aurora Polaris - Polar lights - Polarlys(Norwegian) (both northern and southern lights)

What are northern lights?

  • What causes them?

  • Northern lights originate from our sun. During large explosions and flares, huge quantities of solar particles are thrown out of the sun and into deep space. These plasma clouds travel through space with speeds varying from 300 to 1000 kilometers per second.
    But even with such speeds (over a million kilometer per hour), it takes these plasma clouds two to three days to reach our planet. When they are closing in on Earth, they are captured by Earth's magnetic field (the magnetosphere) and guided towards Earth's two magnetic poles; the geomagnetic south pole and the geomagnetic north pole.

    On their way down towards the geomagnetic poles, the solar particles are stopped by Earth's atmosphere, which acts as an effective shield against these deadly particles.
    When the solar particles are stopped by the atmosphere, they collide with the atmospheric gases present, and the collision energy between the solar particle and the gas molecule is emitted as a photon - a light particle. And when you have many such collisions, you have an aurora - lights that may seem to move across the sky.
    In order for an observer to actually see the aurora with the naked eye, about a 100 million photons are required.

    Coronal Mass Ejection (CME) is another word for the gigantic explosions and flares that occurs on our sun.

  • The Sun and its impact

  • The Sun

  • Source of life and auroras.
    The Sun, a burning gas globe, has provided life-giving light and warmth to our earth for nearly five billion years.
    The Sun's energy originates in its interior, where the temperature exceeds 15 million degrees Kelvin (K), and the pressure is 250 billion times greater than on the earth's surface. Here the tremendous heat transforms hydrogen, the lightest element in the known universe, into helium. The sun's surface has a temperature of approximately 5800 K.

  • Solar maximum

  • The solar activity varies over periods of approximately 11 years. When the number of spots peak, we have what is referred to as solar maximum, and likewise solar minimum when the sunspot activity is low. The more sunspots, the more solar particles are ejected out into deep space and thus more auroras occur on earth. The latest solar maximum was in 2001-2002, the next is expected some time around 2011-12.

  • Sunspots

  • Sunspots are patches created by strong magnetic fields on the surface of the sun. Since these areas are somewhat cool compared to their surroundings (about 1000 degrees cooler), they appear darker. Sunspots are visual indications of the process that sends charged particles into space. These particles may be captured by earth's magnetic field to create the aurora.

  • Solar Wind

  • A gas of electrons and ions - at supersonic speed - is continuously emitted from the sun. This stream of gas is called the solar wind.
    The solar wind is filled with gusts and gales, and when a strong eruption from the sun hits earth, the stable situation - which may have existed for several days - is strongly disturbed. The most spectacular result of this interaction is an intense aurora significantly closer to the equator than during normal conditions.

  • The Aurora Oval

  • The auroral zones represent the places on earth where auroras occur most often and with greatest intensity. It was the Swiss physicist Herman Fritz (1829-1902), in the 1881 book "Das Polarlicht." who first showed that the northern lights have a maximum zone close to 67 degrees north. He called this belt the auroral zone. Thus, the auroral zones encompass the statistical distributions in latitude of all visible, night side auroras. The more detailed location of the auroral zones is based on professor Størmer's extensive auroral observations between 1910 and 1950.
    The momentary, instantenous distribution of the auroras as a function of both latitude and local time were mapped by ground, rocket and satellite measurements in the 1960s. The best overview was obtained by satellite photos of the earth. Then it was discovered that the auroras display a continous oval zone around the magnetic pole in both hemispheres. Thus the auroral ovals are the regions on earth where the auroras are seen most often and with the greatest intensity.
    The auroral oval is nearly twice as wide and twice as far from the magnetic pole at midnight as at midday, about 23 degrees and 12 degrees, respectively. On the night side the oval is roughly 10 degrees (about 1100 kilometres) closer to the equator than at the day side.
    The auroral oval can be regarded as fixed in space with reference to the sun. As the earth revolves underneath, the daily variations in the aurora's position occur. In the Scandinavian sector you find that Andøya Rocket Range is located under the oval at night, while the oval lies across Svalbard during daytime. Halfway between northern Norway and Svalbard, northern lights can be observed in zenith both morning (around 0600) and evening (around 1800).
    Modern studies have clearly shown that the shapes and locations of the ovals vary greatly with solar activity. With increasing activity on the sun, the oval widens and spreads, mainly towards the equator.

    To continue checking out this and more please visit The Northern Lights Website


    Post a Comment

    << Home