A Beautiful Curtain of Color in the Night Sky: The Aurora Borealis

Author: Suhani Patel

Editors: Tharindi Jayatilake and Cynthia Zhang

Artist: Doris Tan

You gaze up and see the most beautiful colored lights shimmering across the Alaskan night sky. It is a dancing array of neon beauty on a dark moonless night. What are these mysterious beauties?

The Aurora Borealis also referred to as the Northern Lights, is a natural light phenomenon in the sky. It is mainly seen in the high-latitude regions around the Arctic and Antarctic. Four main forms of Aurora Borealis can be seen with the naked eye. The first is a mild glow near the horizon. Although this form is visible, it can be hard to distinguish from moonlit clouds because stars can be seen through the glow. The second form is mere surfaces that resemble a cloud-shape. The third form, arcs, curve across the sky. The fourth form is rays, which are light and dark stripes across arcs. Other types include curtains, which are often caused by folds within the arc. On some rare occasions, an arc may break up into several rays that occupy the whole sky. These forms are also known as discrete auroras, which are the brightest forms. The shapes of the brighter parts of the atmosphere and the position you view the lights determine the appearances of arcs, rays, and curtains. The northern lights offer an entrancing, dramatic, and magical display that fascinates all who see it. So, what causes this dazzling natural phenomenon?

At the center of our solar system lies the sun, a sphere of hot plasma that is the most crucial energy source for life on Earth. The sun's many magnetic fields twist and change position as it rotates on its axis. When these fields become knotted together, they explode and create so-called sunspots. Sunspots are temporary phenomena on the sun's photosphere that appear as spots darker than the surrounding areas. Usually, they occur in pairs; the largest can be several times the size of Earth's diameter. At the center of the sun, the temperature is 27 million degrees Fahrenheit (15 million degrees Celsius). As the heat on its surface rises and falls, the sun boils and bubbles. Particles escape from the star from the sunspot regions on the surface, hurdling particles of plasma, known as solar wind, into space. It takes these winds around 40 hours to reach Earth. When they do, they cause the formation of the Aurora Borealis.

Auroras occur not only on Earth but also on gas giants in our solar system (Jupiter, Saturn, Uranus, and Neptune). However, auroras formed on them are different, given that they form under thicker atmospheres and stronger magnetic fields.

Venus has an aurora generated by its stretched-out magnetic field, known as a magnetotail. Mars, which has too thin an atmosphere for global auroras, experiences local auroras due to magnetic fields in the crust. NASA's MAVEN (Mars Atmosphere and Volatile Evolution) spacecraft also found widespread northern hemisphere auroras generated by energetic particles striking the Martian atmosphere. The sunspots and solar storms that cause the most magnificent displays of the northern lights occur roughly every 11 years. The solar cycle peaked in 2013, but it was the weakest solar maximum in a century. There have been 22 full cycles of the ebb and flow beginning in 1749. Researchers monitor space weather events because they can affect spacecraft in orbit, knock out power grids and communication infrastructure on Earth, and amp up typical displays of the northern and southern lights. Scientists are also investigating how fluctuations in the sun's activity affect weather on our planet. Debris, radiation, and other magnetic waves from space that threaten the future of living beings continuously bombard Earth. Most of the time, the planet's magnetic field does an excellent job of deflecting these potentially harmful rays and particles, including those from the sun.

The Aurora Borealis phenomenon in Iceland. (Lewis, 2018)

Particles discharged from the sun travel 93 million miles (around 150 million kilometers) toward Earth before they are drawn irresistibly toward the magnetic north and south poles. As the particles pass through the Earth's magnetic shield, they mingle with atoms and molecules of oxygen, nitrogen, and other elements that result in the dazzling display of lights in the sky.

Aurora Borealis can appear in a variety of different colors. Most are green in color, but sometimes you’ll see a hint of pink, and strong displays might also have red, violet, and white colors. The lights typically are seen in the far north in the nations bordering the Arctic Ocean (Canada and Alaska, Scandinavian countries, Iceland, Greenland, and Russia). But strong displays of the lights can extend down into more southerly latitudes in the United States. And of course, the lights have a counterpart at Earth’s south polar regions. The colors in the aurora are also a source of mystery throughout human history. But science says that different gases in Earth’s atmosphere give off different colors when they are energized. 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 impacts the colors that appear in the sky. Atomic nitrogen causes blue displays, while molecular nitrogen results in purple. Altitude also plays a factor. The green lights typically in areas appear below 150 miles (241 km) high; red lights appear above 150 miles; blue lights appear below 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.

Humans have been fascinated by the waxing and waning of auroral lights from prehistoric times, the closest and most dramatic manifestation of space phenomena. Spectacular auroral eruptions have given rise to mythological creatures, have driven folklore, and have influenced the course of history, religion, and art. There have been, and still are, many different beliefs about the aurora and its association with the spirit world. Stories come from the Northern reaches of Alaska, Canada, and Greenland telling of people's whistling bringing down the aurora to cut the whistler's head, and of auroras as spirit ancestors to help hunters find their prey. 'Aurora Borealis,' the lights of the northern hemisphere, means 'dawn of the north.' 'Aurora australis' means 'dawn of the south.' Many cultural groups have legends about the lights. In Roman myths, Aurora was the goddess of the dawn. In medieval times, the occurrences of auroral displays signaled harbingers of war or famine. The Maori of New Zealand shared a belief with many northern people of Europe and North America that the lights were reflections from torches or campfires. The Menominee Indians of Wisconsin believed that the lights indicated the location of manabadi wok (giants), the spirits of great hunters and fishermen. The Inuit of Alaska believed that the lights were the spirits of the animals they hunted: the seals, salmon, deer, and beluga whales. Other aboriginal peoples thought that the lights were the spirits of their people.

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