Auroras: The Science Behind Nature’s Light Shows
By Parul Pahurkar
Cosmofluencer (Season 04)
The night sky has always interested human beings: the twinkling stars, the glowing beauty of the moon, and sometimes the rare and magnificent display of colored lights shimmering across the heavens—auroras. Breathtaking and surreal, these almost fantastical light displays known as the Northern Lights (Aurora Borealis) in the North and the Southern Lights (Aurora Australis) in the South. But what exactly are auroras, and what causes this eye-catching phenomenon? From where can we observe it?
What are Auroras?
An aurora is a natural light show that appears in the polar regions of Earth, close to the polar circles of the Arctic and Antarctica. The phenomenon is the interaction of solar wind-a stream of charged particles (mostly electrons and protons) from the outer atmosphere of the Sun-with the magnetic field and atmosphere of Earth, causing phenomenal lights at Earth’s zenith which is a point in the sky that is directly above an observer, at a 90-degree angle from the ground). When these charged particles collide with the gases in the outer atmosphere of Earth, they create glowing curtains of light that ripple and dance across the sky.
The northern lights above Iceland. (Image credit: Chalermkiat Seedokmai via Getty Images)
The Colors of the Auroras
These wonderful colours of the auroras depend on the kind of gas molecules these solar particles, which originate from solar flares and coronal mass ejections (CMEs) when intense magnetic activity on the Sun’s surface accelerates and releases charged particles into space, hit and at what altitude such collisions take place:
- Green Auroras: The most common colour is green, resulting from charged particles hitting oxygen molecules at lower altitudes around 60 miles or 100 km above the Earth.
- Red Auroras: These are rarer in appearance but equally startlingly beautiful. They form themselves when solar particles interact with oxygen some 200 miles up in the atmosphere.
- Blue or Purple Auroras: Blue or purple colouring occurs when solar particles interact with nitrogen, occasionally at lower altitudes.
- Yellow and Pink Auroras: These are mixed between red, green, and blue, creating more complex and rare colour variation. The pink colour of the aurora is because of
Where and When can you See Auroras?
Auroras are primarily viewed near Earth’s magnetic poles-the polar regions of the North, which is the Arctic, and of the South, which is the Antarctic. The best vantage points to see the light spectacle occur are in regions situated near these poles:
● Northern Hemisphere: Alaska, Canada, Norway, Sweden, Finland, and Russia.
(sadly, not India)
● Southern Hemisphere: Even in southern parts of Australia, New Zealand, and Antarctica, auroras are as accessible, though much less so, for sighting.
Hence, the time to observe aurorae is during the nighttime in winter since nights are long and nights are dark.
How do the Northern Lights Form?
The Northern Lights are the outcome of interaction between the charged particles from the Sun and Earth’s magnetic field and atmosphere. Here’s how it occurs:
- Solar Wind
The Sun constantly emits a stream of charged particles, known as electrons and protons, each and every time.
During solar storms or eruptions like the solar flare and coronal mass ejection (CME), solar wind is denser that mostly brings more particles to Earth.
- Earth’s Magnetic Field
The Earth has around it a magnetic field that protects us from the majority of the particles of the solar wind.
This field sends most of the solar particles away from Earth, while some particles follow along the magnetic field lines to the polar regions.
- Collision with Earth’s Atmosphere
Near the North and South Poles, magnetic field lines bunch together there and provide openings for some charged particles from the solar wind to penetrate Earth’s upper atmosphere.
Upon colliding with atoms and molecules within the atmosphere, these particles lose their energy, exciting the atoms and molecules to higher energy levels.
- Light radiation
The energy lost during collisions is released when atoms and molecules return to lower energy levels.
When the added energy is lost and returned to normalcy, the atoms and molecules emit light, which we see as these colorful glowing structures commonly referred to as auroras.
Auroras on Other Planets
A composite image of Jupiter taken by Webb’s NIRCam, showing the planet’s rings and two of its moons, Amalthea and Adrastea. The blue glow around Jupiter’s poles is the aurora. (Image credit: NASA, ESA, CSA, Jupiter ERS Team; image processing by Ricardo Hueso (UPV/EHU) and Judy Schmidt.)
Auroras do happen on other planets as well. All it takes to create an aurora is an atmosphere and a magnetic field.
“Auroras have been seen in the atmospheres of all the gas giant planets, which isn’t surprising since these planets all have strong magnetic fields,” said Jeff Regester, instructor of physics and astronomy at High Point University in North Carolina. “Surprisingly, though, auroras have also been found on both Venus and Mars, neither of which have a very strong magnetic field at all.”
Actually, researchers have identified three distinct types of Martian auroras. One occurs only on the dayside of the planet, while another is a more widespread feature at night which is driven by very strong solar storms and another is much more patchy nightside phenomenon.
The Hope Mars orbiter, which is the United Arab Emirates’ first interplanetary mission, has been able to catch the spotty nighttime aurora just weeks after it reached the Red Planet in early 2021. The observations by the probe might help scientists better understand the phenomenon.
Jupiter’s magnetic field is 20,000 times stronger than Earth’s so auroras that blaze around that gas giant planet are much more vivid and impressive. And here’s the stunning part: These Jupiter lights aren’t just being driven by the solar wind: Most of the particles that cause the planetary auroras are actually blasted into space by Jupiter’s close-orbiting moon Io – the most volcanic body in the solar system.
Astronomers have even caught a glimpse of what they believe to be auroral activity in other solar systems. In fact, two studies published in October 2021 reported that they detected radio waves being emitted by several red dwarfs – stars smaller and dimmer than our sun.
These radio waves are potentially associated with a kind of “reverse” aurora: activity that seems to occur around the stars instead of at their poles, and is fueled by particles released by close-orbiting planets, scientists said.
Conclusion
In a nutshell, auroras are among the most colorful and captivating displays of our Earth and further out in space, reaching us with secrets of the cosmos. These streams of glistening lights originate from the complex dance between solar wind particles and Earth’s magnetic field, causing atoms in the atmosphere to ignite in order to produce colors that ripple across the sky. They can be seen on Earth, on polar regions, but the same kind of auroras are seen on other planets, and maybe even on stars, making them universal phenomena. Auroras remind one of the dynamic connections that exist between the Sun and planets and the invisible forces which shape our skies, a glimpse into the fantastic beauty of the universe.
References
1. Northern lights (aurora borealis): what they are and how to see them | Space.com
2. What Is an Aurora? | NASA Space Place
3. Auora | Wikipedia
4. Aurora | National Geographic