Description: Near the poles of Earth, observers have often seen glowing clouds shaped like curtains, tapestries, snakes, or even spectacular radiating beams. Northern Hemisphere observers call them the Northern Lights of Aurora Borealis. Southern Hemisphere observers call them the Southern Lights or Aurora Australis. Because most people, and land masses, are found north of the equator, we have a longer record of observing them in northern regions such as Alaska ,Canada, Scandinavia, but sometimes as far south as the Mediterranian Sea or Mexico!
Sprinkle iron filings on a paper and put a magnet underneath. You will see lines of magnetism that seem to 'flow' towards the poles of the magnet. If you were a charged particle in space, you would be magnetically trapped on one of these lines of magnetism. As you flow down Earth's magnetic field into the north and south poles, you collide with atoms of oxygen and nitrogen. This gives off the colored lights you see in an aurora. What do you think these ovals of light look like from the ground if you were looking up at the sky? From space we can look down at an aurora and see that it actually looks like a crown of light! Scientists call this the Auroral Oval (see below satellite photo from IMAGE). If you were standing on the ground looking up at the night sky, you would only see a very small part of this halo. It would look like beautiful draperies and curtains of shimmering light that change shape from minute to minute!
Watch a Aurora Movie I
Watch a Aurora Movie II
Look at an Enlarged Picture
Causes:
The most common explanation you will find in print is that particles from the Sun flow down the magnetic lines of force into the polar regions of Earth. They collide with oxygen and nitrogen atoms in the atmosphere which emit the colored lights we see in the aurora. This explanation is actually incorrect, although it is easy to describe in a few brief sentences, which is why it is popular in many textbooks.It has been known for decades that the correct explanation for why aurora occur involves distant regions of the magnetic field of Earth in the opposite direction from the Sun. As solar storms disturb Earth's magnetic field, this field rearranges itself and converts some of its stored energy into the kinetic energy of fast-moving particles. These particles, partly from the Sun and partly from Earth, flow inwards towards Earth along the polar magnetic field lines. As they encounter the ionosphere, they are boosted in energy to 6,000 volts or more, and then collide with nitrogen and oxygen atoms to produce the auroral light. There is no direct entry of solar particles into the polar regions to create the night-time aurora. Also, solar flares do not cause aurora either.
Watch an IMAGE Aurora Movie
Watch an Polar Aurora Movie
Look at an Enlarged Picture
Properties:
There are aurora over both poles of Earth almost every day, but they are mostly too faint to see. The two satellite views below show the aurora over the North (left) and South (right) polar regions on June 30, 2003. Notice how similar they are in shape and brightness - this shape similarity is what scientists call Auroral Conjugacy. Aurora are formed in the atmosphere at elevations from 100 to 1000 kilometers where the density of the air is very low - in fact almost a perfect vacuum. Enormous amounts of electrical energy are produced during an aurora when millions of amperes of electric currents pass through the atmosphere and generate nearly 900 billion watts of energy - mostly in heat but about a few percent in light.
Picture Gallary
Many people enjoy the challenge of photographing the aurora. It's actually very easy to do this, but if you really want drop-dead photos you have to use cameras that let you take exposures several seconds long, and with wide-angle lenses. Most drug-store cameras and even digital cameras do not work well. Here are some spectacular images captured by professional photographers, and by NASA astronauts and satellites too!
What Alaskan students say:
One of the best sources of information about the aurora is Alaskan students who write essays about them for us to enjoy!