Most of us have never observed the Northern Lights in person, but many will have seen images of this spectacular event. But what exactly is this phenomenon also known as the Aurora Borealis?

It is probably one of nature’s most breathtaking displays, but due to its location, few of us ever get to see an Aurora Borealis occurrence. Situated over the Arctic region, this phenomenon has also been the source of many awe-inspiring photographs.

This article examines what this multicolored light display is and also how it occurs. It also looks at the facts and characteristics that define it.

Several different factors are involved in the creation of the Aurora Borealis, and their interactions with each other result in the occurrence of this optical phenomenon. Before examining it in more detail, one needs to obtain a more elaborate definition of this event.

The introduction already provided a brief description of what the Aurora Borealis is, but one needs a more detailed and concise explanation of this occurrence before continuing.

Aurora Borealis Definition

The Aurora Borealis (or Northern Lights) is a natural atmospheric phenomenon that occurs over the Arctic Circle at a height of approximately 90 – 150 km (56 – 93 miles) above the planet’s surface. It appears as bands or curtains of multicolored lights (predominantly green, violet, and pink).

It is the result of charged particles in solar winds that collide with gas molecules in the upper atmosphere (specifically the thermosphere and exosphere). The resulting ionization of particles is what causes the visual light display over polar regions.

The name, Aurora Borealis, is derived from the names of gods in Roman Mythology. “Aurora” was the Roman goddess of dawn, while “Boreas” is the god of the north wind. The term was coined by Galileo Galilei, an Italian astronomer, in 1619.

In Norse Mythology, the Aurora Borealis was believed to be a bridge made of fire that extended into the sky.

This phenomenon also goes by several names, including the Northern Lights, Polar Lights, Merry Dancers, and Aurora Polaris. It also has different names when it occurs in the Southern Hemisphere over Antarctica, but more on that later.

The primary colors that are displayed are luminous green, violet, and pink. It also produces hues of blue, yellow, and occasionally white and orange.

When particles collide with nitrogen, the result typically produces deep red and violet colors. When a collision between charged particles and oxygen occurs, though, it produces the colors green and yellow.

The Aurora Borealis occurs in the magnetosphere, the magnetic field that surrounds and protects the Earth from incoming solar winds. It starts several hundred kilometers above the Earth’s surface but extends further than 600,000 kilometers (370,000 miles) in altitude.

(It should not be confused with Earth’s 5 atmospheric layers, though, which are categorized according to air density, temperature, meteorological activity, and gravitational force. Technically, the magnetosphere starts in the thermosphere and extends into outer space.)

The following steps will serve to illustrate how exactly the Aurora Borealis forms and develops:

1. 1. The Aurora Borealis starts more than 148 million kilometers (92 million miles) away in the center of our solar system, where the Sun produces a wave of charged particles called solar wind that travels to the Earth.
   2. Solar wind is a result of sunspots that occur when magnetic fields on the Sun’s surface collide and release energy, sending charged particles into the solar system.
   3. As the solar wind reaches the outer limits of Earth’s atmosphere, it comes into contact with gas molecules in the upper atmosphere.
   4. Charged particles from the solar wind collide and interact with the gas molecules, transforming them into a higher state of energy.
   5. When the atoms in the gas molecules get energized, the electrons in the atoms move further away from their nucleus. 
   6. When they return to their rested state, the electrons emit light particles called photons that result in the light display we view as the Aurora Borealis.
   7. When a nitrogen molecule is energized, it produces colors with a deep red and violet hue. When an oxygen molecule is energized, it produces the colors green and yellow.  

There are other and more detailed processes involved as well, but these steps capture the essence of how the Aurora Borealis forms.

1. 1. Diffused light appearing close to the horizon that may be hard to observe.
   2. Bands of light that are similar to arcs but with more of a curvature.
   3. Arcs appear that extend across the sky.
   4. Rays are curtain-like light and dark stripes extending into the sky.
   5. Coronas cover vast portions of the sky and extend from horizon to horizon.

There are, of course, many other types and variations of this phenomenon, but at the core level, they can be broken down into these 5 types of Aurora Borealis.

Although we are very familiar with the Aurora Borealis (or Northern Lights), this phenomenon actually occurs over the polar regions of both the Northern and Southern Hemispheres.

If it occurs in the Southern Hemisphere over Antarctica and surrounding regions, it is known as Aurora Australis or Southern Lights.

In both hemispheres, Auroras are approximately 3 to 6 degrees in width. They are located between 10° and 20° from the geomagnetic poles.

In the Northern Hemisphere, they can be seen in the Arctic Circle and northern countries bordering it. In the Southern Hemisphere, they can be observed over Antarctica, the southernmost part of Argentina, Australia, and New Zealand.

In earlier sections, the definition and formation of the Aurora Borealis were already established. The following list, though, highlights the key facts and characteristics surrounding this phenomenon:

1. 1. The Aurora Borealis is a result of charged particles in solar wind colliding with gases in the upper atmosphere.
   2. The ionization of gas molecules results in the multicolored display over regions in the Arctic Circle.
   3. The primary colors of the Aurora Borealis are luminous green, violet, and pink.
   4. There are 5 types of Aurora Borealis, categorized according to size and brightness.
   5. The Aurora Borealis occurs in the magnetosphere, Earth’s magnetic field that protects the planet from solar wind.
   6. According to Norse Mythology, the Aurora Borealis was believed to be a bridge of fire that reached into the sky.
   7. It appears at an altitude of 90 – 150 km (56 – 93 miles).
   8. It can extend to over 1000 km (621 miles) above the Earth’s surface. 
   9. This phenomenon occurs over both poles in the Southern and Northern Hemispheres. It is called the Aurora Australis (or Southern Lights) when it forms over Antarctica.
   10. It occurs between 10° and 20° from the geomagnetic poles.
   11. Some observers claim there are sounds associated with the Aurora Borealis, although this claim has not been scientifically proven yet.
   12. It is clearly visible from space. Some of the most interesting images, putting their size and scale in perspective, have been taken from the International Space Station (ISS). 
   13. It occurs on other planets, including Jupiter, Saturn, Neptune, and Uranus.

This is not a complete and exhaustive list but highlights the most important and relevant facts about the Aurora Borealis.

Although the Aurora Borealis continuously occurs in the upper atmosphere, it is only visible under certain conditions and in specific regions of the world.

The Northern Lights are most commonly seen in areas close to the Arctic Circle. Countries like Norway, Sweden, Finland, Iceland, Canada, and Alaska are among the best places to observe this phenomenon.
To view the Aurora Borealis clearly, dark and cloudless skies are crucial. This is why the winter months, when nights are longer and darker, are the best time to witness the display.

Another important factor is solar activity. Strong solar wind significantly increases the chances of auroral activity, resulting in brighter and more widespread displays.

Although rare, the Northern Lights can occasionally be seen further south when solar activity is particularly intense.

As this article clearly illustrates, the Aurora Borealis is a natural atmospheric phenomenon that occurs on a gigantic scale (literally extending hundreds of miles into the edge of space), producing truly breathtaking light displays.

But as also explained, it is a natural phenomenon with a clear scientific explanation that has been widely researched throughout the last few centuries. And today, we understand even more about the Aurora Borealis than ever before.

It may not be the “fire bridge to the sky” as the North Germanic people believed, but that does not take anything away from the feelings of awe and magic this spectacular phenomenon evokes.

Until next time, keep your eye on the weather!