Understanding

  Aurora 101  

     In one easy step (Aurora 101)
     or a few more detailed steps (Aurora 202)

  This web site is a compendium of information from several web sites listed at the end of this article.

Aurora 101

How:
In a nutshell, aurora occurs when charged particles from the sun hit the earth's atmosphere and cause the air to glow.

Where:
Aurora occurs 100-300 km above the earth in the aurora oval, a circle a few thousand kilometers in diameter around each of the earth's magnetic poles. Northern Canada, Alaska and the extreme north of Europe and Asia are the most common places to see aurora. Occasionally, the oval will expand and aurora can be seen further south in places like the United States and central Europe and Asia.

When:
Some aurora is in the oval all the time but it is usually too faint to see. The best time to look is within a couple of hours of midnight on clear, moonless nights, away from city lights. The globe below shows you how often you're likely to see aurora from various parts of North America. Sometimes aurora can be predicted. More on that in Aurora 202.

This has been a quick overview. If you want a more detailed explanation see ... Aurora 202

To photograph the aurora

You'll need:

• a camera that can take long exposures - up to 30 seconds. Most SLR cameras and a few point and shoot cameras can do this.
• a reasonably fast, normal or wide angle lens. f/2.8, 35 mm is OK. Smaller numbers such as f/2 or f/1.4 and 28mm or 24mm are better.
• a tripod
• a cable release or a self-timer on the camera
• If your camera uses film, ISO 400 is OK. ISO 800 is better
• your camera manual - so you can find out how to set up the camera for these exposures. If you can't find it, download a copy from the manufacturer's web site.

If it's cold:

• a pair of thin gloves to operate the camera when it is cold
• a plastic bag to put your camera in so condensation will not form on it when you bring it into the warmth.

Aurora varies in brightness so there is no one exposure time that works for all cases. Try the suggestions listed below and bracket widely (that is, take several pictures with different exposure times. Try 1/4, 1/2, and 2 times what is suggested below). Set the focus to infinity.

Exposure Times (seconds):

Very bright aurora photographed with a Sony DSCW1 digital camera: 10 seconds at f/2.8, ISO 400.

More aurora images

On to Aurora 202

Links for some of the material in this article and for further reading:

http://www.birchwoodtours.com/aurora/52/default.aspx

http://www.gi.alaska.edu/asahi/color.htm

Send comments and suggestions to Chris Brown

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