The Northern Lights are one of the most well-known sights in and around the Arctic Circle. Attracting thousands of tourists every year, the Northern Lights, also known as the aurora borealis, causes the night sky to light up in a panoply of spectacular colors, a phenomenon that can occur anywhere in the world but is most common at and near the North and South Poles. But some people may be wondering why the Northern Lights light up in specific colors and not others.
A natural phenomenon caused by the Earth’s interaction with the sun, the colors of the Northern Lights depend on a number of factors, including altitude and which types of air molecules are involved. Read on to discover how the colors of the Northern Lights work.
The Colors of the Northern Lights and How They Work
The Northern Lights are caused when solar wind, the term used for particles regularly emitted by the sun, collides with the magnetosphere, the protective field surrounding Earth that is generated by the magnetic North and South Poles. When solar wind impacts the magnetosphere, the interaction between the two creates auroras, with the colors of the Northern Lights determined primarily by the altitude at which solar wind collides with the magnetosphere and which types of air molecules are present in the surrounding atmosphere.
The effect is not dissimilar to that of a neon sign. Neon lights work by using electricity to excite molecules, with the resulting chemical interaction giving off light. Similarly, solar wind is primarily comprised of charged particles that give off light upon impact with the Earth’s atmosphere. This process is slightly different depending on existing solar activity as well as which band of atmosphere the solar wind is able to penetrate.
The Earth’s atmosphere is primarily composed of nitrogen and oxygen, with varying levels of both depending on altitude. Because of this, the most common types of auroras are green auroras, which are created when solar wind interacts with oxygen and nitrogen molecules in the lower atmosphere. Blue auroras are less common and result from solar wind penetrating into lower bands of the atmosphere where oxygen is rare or nonexistent.
Solar activity is also a factor in the color of the Northern Lights, with exceptionally high levels of sunspot activity generating red auroras from time to time. These occur when solar wind interacts with nitrogen in the outermost bands of the atmosphere. There are also ultraviolet and infrared auroras; the former can be sometimes seen with the naked eye but are rare and difficult to spot, while the latter cannot be seen without the requisite monitoring equipment.
Another, rarer occurrence are yellow, pink, and purple auroras. These occur when solar wind is able to penetrate multiple layers of the atmosphere, resulting in primary color auroras mixing at the margins. Due to red, yellow, pink, purple, and other auroras requiring exceptional levels of solar activity to manifest, it is unlikely that you will see one on your Northern Lights adventure, though you should never rule them out, either.
As a rule, green auroras occur when solar wind penetrates to a maximum height of 150 miles (241 kilometers) above the Earth’s surface. Red auroras occur at elevations beyond 150 miles, while blue auroras appear at up to 60 miles (96.5 kilometers). Purple, pink, and yellow auroras occur at heights above 60 miles.
As an additional corollary, even visible auroras can only be seen in a small manner due to the limitations of human eyesight. While the Northern Lights remains a spectacular sight in person, many bands of light and particles are invisible to the naked eye and thus can only be picked up by cameras or specialized equipment. Don’t let that dissuade you from taking a trip to the Arctic Circle and witnessing an aurora for yourself.
As a phenomenon dependent on many external factors, the exact colors of the Northern Lights are hard to predict. Green auroras are the most common by far, but it is also possible to see blue, red, and other colors of aurora depending on solar activity. While scientists have tracked solar activity and its peaks and valleys for decades, it remains somewhat unpredictable, so there’s always the chance you could see a rare aurora while on your Northern Lights sojourn.
Having said that, the Northern Lights remains a spectacular sight no matter which colors are visible on any given night. As one of the premier natural sights of the Arctic Circle, the Northern Lights is an experience you will remember for the rest of your life. Watching the night sky come alive in an array of colors is an experience you can only have in the far northern parts of the world. If you’re curious, why not book a tour up north and see for yourself?