Tuesday, November 8, 2011
Chasing The Aurora Borealis
The Northern Lights are in a period of increased activity, and now is the ideal time to be out photographing this dance in the sky
The Northern Lights are caused by charged particles thrown off by the sun during periods of intense solar activity. As these particles, e.g., the "solar wind," enter the Earth's atmosphere, they excite the gas molecules in our upper atmosphere, primarily oxygen and nitrogen, causing them to emit light. The more powerful the solar activity, the brighter and more lively are the resulting auroras here on Planet Earth.
Although auroras can appear to dance just overhead, they actually happen very high above the Earth, from 50 to 200 miles up. Most are lime green in color, but also can turn intense shades of purple and red. Keep in mind, though, that not all of the aurora color is visible to the human eye. Some of the intense reds you see in pictures are much less vivid in person, but are intensified with camera time exposures.
Where To Go
The best aurora viewing is within a donut-shaped band, the Auroral Oval, that circles both ends of the globe (the Southern Hemisphere has its own show called the Southern Lights, or Aurora Australis). The Oval passes directly over places like Fairbanks, Alaska, Yellowknife, Canada, and Reykjavik, Iceland, making all three excellent choices for auroras. During periods of intense auroras, the Oval expands, allowing the lights to be seen over a wider area. It takes a truly massive display, which may happen no more than once or twice a year, for the aurora to be visible in the Lower 48.
When To Go
The aurora can occur any time of year, but in the Land of the Midnight Sun, you're not going to see much between May and September. Just why this should be the case isn't entirely clear, but whatever the reason, these seasons also have the benefit of longer days and milder weather, and offer more things to do when not gazing skyward.
The greatest challenge for sky-watchers is the weather, of course. You can easily spend a week staring up at the bottom of a solid bank of clouds, tortured by the certainty that there's a dazzler going on somewhere up there, but you can't see it. When picking a location, check weather data to see what months tend to have more cloudless nights and then keep your fingers crossed.
Some people prefer to avoid the full moon, whose brightness can diminish the intensity of aurora displays, but moonlight can add a wonderful luminosity to a snowy landscape.
The truth is, the best time to go after auroras is when something is happening on the surface of the sun, a fact that makes it difficult to plan a trip very far ahead. There are a number of websites that track sunspots and "solar weather" and can help predict aurora activity. If you're flexible, wait until you see a stretch of clear weather in the forecast and snag a cheap, last-minute flight north.
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