Photo courtesy of Kakslauttanen
Simply put, the Aurora Borealis and Australis are the Northern and Southern Lights. These mesmerizing, beautiful green, blue, red and purple lights that flash over the polar skies. As we move into the winter months, they become more and more visible in the polar regions.
Have you ever wondered what these "lights" really are? I never put a lot of thought into it until I listened to a presentation by a photographer who was taking a group to Norway. Not being a scientist, the discussions around solar flares, magnetic fields, electrons and who knows what else could have made my brain go blurry. I appreciated his simple presentation in layman's terms, and found all of it to be quite fascinating. I'm certain you will too.
A string of events occurs in order for there to be an aurora. It all starts with the sun.
The sun is an active star, made up primarily of hydrogen and helium. These gases erupt and cause solar flares, which throw out electrons which follow Earth's magnetic fields to the polar regions. (If it weren't for these magnetic fields, the Earth would literally "burn up". Very simply, the magnetic fields protect the Earth from the harmful ultraviolet rays from the sun.)
However, over the polar regions, there are small, natural holes where these gases have a "back door" to get in to the Earth's atmosphere . The electrons collide, if you will, with other natural gasses in the Earth's atmosphere, nitrogen and oxygen. The energy released from the collision is seen in the form of light - the auroras.
The auroras typically form 50-300 miles above the Earth's surface. The height of the collision and what chemicals are in the atmosphere at the time determine the colors you see.
Green is by far the most prevalent - electrons hitting a mixture of nitrogen and oxygen 150+ miles up in theatmosphere. Red colors come about with more nitrogen in the atmosphere. Yellow is actually a mixture of green and red, about 37 miles in altitude. Blue is caused by ionized nitrogen 60 miles up in the atmosphere, and purple is nitrogen colliding, also 60 miles up.
One last thing about auroras. There are generally three types: an "arc" - overhead lights that don't move much, "curtains", which move like curtains in a slow wind. The last type is a corona (below), which is a curtain that passes right above you - the brighter it is the faster it moves. This is is the type of aurora you really want to see. Very dramatic!
The Aurora Australis can be seen primarily from the Antarctic region. Since this is a less visited region, most auroras are seen by travelers in the northern Arctic regions, places like Alaska, Canada including the Northwest Territories, the Yukon and Nunavut, as well as the Lapland region, Greenland and Iceland.
The photographer was escorting a group on a Hurtigruten Norway cruise Past cruises had delighted passengers with nightly aurora shows, like the one below. Lapland has the spectacular Kakslauttanen hotel (first picture) where you can observe the lights in your own glass igloo. How fun is that!
Although the auroras occur year round, they can only bee seen in dark, clear skies. For this reason most sightings are October through April, when the skies are dark and the nights are cold.
NOTE: Apologies to all the scientists out there. This is a very simplified explanation, enough to get the idea across. For those interested, there are far more detailed and precise explanations out there!
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