Frequently asked questions about the aurora
with answers by Dr. Syun-ichi Akasofu

What is the aurora?
The aurora appears as lights in the sky which are given off by atoms and molecules in the upper atmosphere when they are hit by high energy electrons.




What causes the aurora?
The aurora is caused by a powerful electrical discharge in the sky, similar to lightning. High energy electrons generated by the discharge hit atoms and molecules in the upper atmosphere, which give off light. The auroral discharge is far more powerful than lightning.


Where can we see the aurora?
The aurora can be seen best along the belt which connects central Alaska, the Great Slave Lakes (Yellowknife) in Canada, the southern tip of Greenland, Iceland, and the northern tip of Scandinavia.

Can we see the aurora in the Southern Hemisphere?
The aurora in the southern hemisphere is known as the aurora australis. It is almost a mirror image of the aurora borealis.



Why does the aurora show different colors?
Different atoms and molecules in the upper atmosphere give off different colored lights. Atomic oxygen gives off greenish and red light. Molecular nitrogen gives off pinkish light.

Why does the aurora move?
The aurora appears where beams of high energy electrons penetrate the upper atmosphere. As the beams move, the aurora moves.




Why can we see the aurora on
cold nights, but not on warm nights?

The aurora occurs well above the altitude of clouds. On cold nights, the sky tends to be clear so that the aurora is visible. Warm nights tend to be cloudy and the clouds hide the aurora.



Can astronauts see the aurora from
the space shuttle?

Yes. The space shuttle flies at an altitude where the aurora is present. Astronauts say that it is spectacular to fly through the aurora.


The aurora seen from the space shuttle



Does the aurora produce a sound?
Technically it should be impossible to hear the aurora from the ground because the lowest edge is 60 miles (100km) away and the atmosphere there is too thin to transmit sound waves. However, reports of whooshing and crackling noises associated with active aurora persist and groups in Denmark and Finland claim to have recorded sounds. A number of theories regarding the perception of auroral noises abound.


Is the aurora harmful?
The aurora can cause a variety of problems. It can disrupt radio communications, damage satellites, and disrupt power stations and power lines resulting in power outages. The high energy electrons that produce the aurora may be hazardous to astronauts in space so they should remain in the spacecraft when it flies through an aurora. Here on Earth's surface we are safe. We live and travel in only the first 14km (8 miles) of Earth's atmosphere, nearly 100km (60 miles) below the aurora. Because of the protective role of the atmosphere, the aurora and the high energy electrons that produce it (under normal conditions) pose no known health risks such as those from radiation or electric shock.




Saturn's aurora
Hubble Space Telescope
Why doesn't the moon have an aurora?
The aurora is caused by electrical discharge powered by the interaction between a magnetic planet and the solar wind (a stream of charged particles flowing out from the sun). To produce an aurora like Earth's, a planet needs a magnetic field and an atmosphere. The moon has neither. Other magnetic planets with atmospheres, such as Saturn and Jupiter, have an aurora.
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site last modified: August 2003 maintained by Asahi Aurora Web Manager