Auroras

Celestial Fireworks

Have you ever gazed up at the night sky and been mesmerized by the dance of colors? If you’re lucky, you might have witnessed one of nature’s most awe-inspiring phenomena—the auroras. This stunning light show has been captivating humans for centuries and continues to draw crowds from around the world. But what exactly are the auroras, and why do they occur?

In the Northern Hemisphere, it’s commonly known as the northern lights or aurora borealis, while in the Southern Hemisphere, it’s called the southern lights or aurora australis. Italian astronomer Galileo Galilei is credited with coining the name “aurora borealis” in 1619, inspired by the Roman goddess of dawn, Aurora, and the Greek god of the north wind, Boreas. However, the earliest record of the northern lights dates back to 2600 BCE in ancient Chinese texts.

The northern lights shine above Bear Lake, Eielson Air Force Base, Alaska, 2005. Credit: United States Air Force photo by Senior Airman Joshua Strang

The northern lights shine above Bear Lake, Eielson Air Force Base, Alaska, 2005. Credit: United States Air Force photo by Senior Airman Joshua Strang

Ancient cultures, such as the Eskimos and Native Americans, believed that the lights were spirits playing with a walrus head, while the Vikings believed the phenomenon was light reflecting off the armor of the Valkyrie, supernatural maidens who guided warriors to the afterlife.

For centuries, the auroras were a mystery to both scientists and the general public. It wasn’t until the turn of the 20th century that Norwegian scientist Kristian Birkeland proposed a groundbreaking theory explaining the science behind this mesmerizing phenomenon.

Brilliant time-lapse of Alaska’s northern lights

Brilliant time-lapse of Alaska’s northern lights

What causes the auroras? In short: the Sun. At any given moment, the Sun emits a stream of electrically charged particles known as the solar wind. As this solar wind reaches Earth, it encounters our planet’s magnetic field, which acts as a protective shield. Without this magnetic field, the solar wind would strip away our atmosphere, making life impossible.

And on Earth, the aurora borealis and australis serve as intermittent reminders of how nice it is to have a protective atmosphere.

Neil DeGrasse Tyson

These energized particles from the Sun collide with Earth’s upper atmosphere at speeds of up to 45 million mph (72 million kph). Earth’s magnetic field redirects these particles toward the north and south poles, where they enter the atmosphere and interact with gas atoms and molecules, creating auroras. This process is similar to how neon lights work: when gas molecules are energized by electrons, they release photons (light) as they return to their original energy state. The color of the light depends on the gas involved, just like the colors of auroras depend on the gases in the atmosphere.

Northern lights and the Moon from southwestern Iceland, 2017

Northern lights and the Moon from southwestern Iceland, 2017

The Earth’s atmosphere mainly consists of nitrogen and oxygen. Green is the most common aurora color, produced when charged particles collide with oxygen molecules at altitudes between 60 and 190 miles (100–300 kilometers). The human eye is most sensitive to green, making it the easiest color to see.

Nitrogen atoms emit purple, blue, and pink, but these colors are less common because nitrogen atoms are harder to energize. Only a significant ejection of solar particles creates such displays. Occasionally, the auroras appear scarlet. This occurs when oxygen is energized by solar particles at very high altitudes, around 180 to 250 miles (300–400 kilometers).

Red and green Aurora in Fairbanks, Alaska, 2007. Credit: Brocken Inaglory

Red and green Aurora in Fairbanks, Alaska, 2007. Credit: Brocken Inaglory

Auroras are most active when the solar wind is strongest. While the solar wind is generally constant, solar weather—caused by the heating and cooling of different parts of the Sun—can change daily. Solar weather is often tracked by observing sunspots, which are cooler, darker areas on the Sun’s surface. These sunspots are associated with solar flares and coronal mass ejections (CMEs). Solar flares are sudden bursts of energy, while CMEs are massive eruptions of solar material. Both of these events increase the solar wind’s intensity. Sunspot activity follows an 11-year cycle, with the most vibrant and consistent auroras appearing during the peak of this cycle.

Interestingly, auroras aren’t unique to Earth. Any planet with an atmosphere and a magnetic field can experience them. Scientists have observed auroras on Venus, Mars, Jupiter, Saturn, Uranus, and Neptune. The magnetic and atmospheric conditions of these planets vary, resulting in different strengths and appearances of auroras. Jupiter’s auroras are particularly impressive. Since its magnetic field is 20,000 times stronger than Earth’s, the auroras there are much larger and more intense.

A composite image of Jupiter’s auroras captured by the Hubble Space Telescope using ultraviolet light. Credit: NASA, ESA, and J. Nichols (University of Leicester)

A composite image of Jupiter’s auroras captured by the Hubble Space Telescope using ultraviolet light. Credit: NASA, ESA, and J. Nichols (University of Leicester)

For those hoping to witness the northern lights, the best place to be is the “auroral zone,” which is roughly a 1,550-mile (2,500-kilometer) radius around the North Pole. This region is where the auroras are most commonly observed, although, during intense solar storms, the phenomenon can sometimes extend further south. The southern lights are a less flashy version of the northern lights. They are seen best from the southernmost lands like Tasmania, New Zealand, and Antarctica.

Whether viewed from the northern or southern hemispheres, or even on other planets, auroras remind us of the dynamic and interconnected nature of our solar system. They vividly highlight the wonders of nature, the fragility of our existence, and the ongoing mysteries that await our discovery.

Words of wisdom

“The optimist thinks this is the best of all possible worlds. The pessimist fears it is true. ” —J. Robert Oppenheimer

“When you change the way you look at things, the things you look at change.” —Max Planck

“Whenever anyone has offended me, I try to raise my soul so high that the offense cannot reach it.” —René Descartes

“Happiness [is] only real when shared” ―Jon Krakauer, Into the Wild

Bibliography

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