The auroras in Earth's Northern Hemisphere are called the aurora borealis. Their southern counterpart, which light up the Antarctic skies in the Southern Hemisphere, are known as the aurora australis.
What causes the colors?
The colors most often associated with the aurora borealis are pink, green, yellow, blue, violet, and occasionally orange and white. Typically, when the particles collide with oxygen, yellow and green are produced. Interactions with nitrogen produce red, violet, and occasionally blue colors.
The type of collision also makes a difference to the colors that appear in the sky: atomic nitrogen causes blue displays, while molecular nitrogen results in purple. The colors are also affected by altitude. The green lights typically in areas appear up to 150 miles (241 km) high, red above 150 miles; blue usually appears at up to 60 miles (96.5 km); and purple and violet above 60 miles.
These lights may manifest as a static band of light, or, when the solar flares are particularly strong, as a dancing curtain of ever-changing color.
History of the auroral lights
For millennia, the lights have been the source of speculation, superstition and awe. Cave paintings in France thought to date back 30,000 years have illustrations of the natural phenomenon.
In more superstitious times, the northern lights were thought to be a harbinger of war or destruction, before people really understood what causes them. Many classic philosophers, authors and astronomers, including Aristotle, Descartes, Goethe and Halley, refer to the northern lights in their work.
As early as 1616, the astronomer Galileo Galilei used the name aurora borealis to describe them, taking the name of the mythical Roman goddess of the dawn, Aurora, and the Greek name for wind of the north, Boreas.
The aurora australis, or the southern lights, occur around the south polar region. But, since the South Pole is even more inhospitable than the North Pole, it is often trickier to view the southern lights
Where to see the lights
The best places to see the northern lights are Alaska and northern Canada, but visiting these vast, open expanses is not always easy. Norway, Sweden and Finland also offer excellent vantage points. During periods of particularly active solar flares, the lights can be seen as far south as the top of Scotland and even northern England. [A Guide for Watching Earth's Auroras]
On rare occasions, the lights are seen farther south. They were first observed by European settlers in New England in 1791. In "Historical Storms of New England," published in 1891, Sidney Perley wrote, "May 15, 1719, the more beautiful and brilliant aurora borealis was first observed here as far as any record or tradition of that period inform us, and it is said that in England it was first noticed only three years before this date. In December of the same year the aurora again appeared, and the people became greatly alarmed, not dreading it so much as a means of destruction but as precursor of the fires of the last great day and a sign of coming dangers."
When to see the lights
The northern lights are always present, but winter is usually the best time to see them, due to lower levels of light pollution and the clear, crisp air. September, October, March and April are some of the best months to view the aurora borealis. The lights are known to be brighter and more active for up to two days after sunspot activity is at its highest. Several agencies, such as NASA and the National Oceanic and Atmospheric Administration, also monitor solar activity and issue aurora alerts when they are expected to put on a particularly impressive show.
Additional reporting by Elizabeth Howell and Nola Taylor Redd, Space.com contributors
