The Aurora: Borealis And Australis
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 on a winter cruise. 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 the atmosphere. 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 the type of aurora you really want to see. Very dramatic!
The auroras actually occur year round but can only be seen in dark, clear skies. For this reason most sightings are late September, October through April in the northern hemisphere and April to October in the southern hemisphere, when the skies are dark and the nights are cold.
Places in the world to see the auroras?
In the north favorite spots include Alaska (Fairbanks), Iceland, Greenland, Canada (Northwest Territories, the Yukon and Churchill), Norway, Sweden and Finland. Lapland has the spectacular Kakslauttanen hotel (first picture) where you can observe the lights in your own glass igloo. How fun is that! In Norway, Hurtigruten sails all winter, offering great options to observe the lights.
In the southern hemisphere, head to Antarctica, Australia (Tasmania, Phillip Island) and New Zealand. The Aoraki Mackenzie Dark Sky Reserve in New Zealand is the largest in the world and the only one in the southern hemisphere. The Aoraki/Mt. Cook area has nearly no light pollution, making it an excellent area for viewing. Invercargill and Stewart Island on the South Island are also favorites.
Original article published Nov. 4, 2017.
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