Aurora borealis: The Lights of the Northern Night Sky.

Our sun is undoubtedly the single most important celestial body in the entire solar system. It accounts for about 99.86% of the total mass of the solar system. But what it actually is? In brief, the sun is a giant fusion reactor. Now, what is fusion? Well in a sense fusion is, you take two ping pong balls and collide them at high speed and that will give you a tennis ball and a ridiculously huge amount of energy. In stars these balls are atoms. 

Our sun fuses hydrogen into helium and the rate is about 600 million tons of hydrogen into helium every second and it happens in the sun's core.

Aurora Borealis.

Sun's core is not where the journey of Aurora Borealis begins. It begins at something called Corona, actually stellar corona. In short, the corona is the outermost part of the sun's atmosphere. You can see CORONA during a total solar eclipse, of course with proper eye protection. 

Sun's Corona during a
total solar eclipse. 
(Credit: Wikipedia)

Sun's corona is surprisingly hotter than the surface of the sun, around one to four million degrees. This much energy is enough to rip atoms apart by exceeding the strong nuclear force(one of four fundamental forces of nature that hold atoms together). Which means free protons, free electrons, and high energy. This is known as the fourth state of matter called plasma.

Every second one million tons of matters is blasted from the sun at the velocity of one million miles per hour. This is also known as the solar wind. And most of them come towards Earth. But we are still safe because of our magnetic field. 

Earth's magnetic field. 
(Credit: Science ABC)

At the core of our planet, there are melted metals. Earth's spin on its axis causes the liquid metals to flow. This flowing of liquid metals generates an electric current. Earth's spin on its axis causes an electric current to form a magnetic field. Earth's magnetic field works as a shield against the solar wind. But this magnetic field is also responsible for auroras to form only on poles. Here is why. After getting released from the Sun, the next stop for the solar wind or plasma is Earth's magnetic field.

Solar wind interacting with magnetic field lines
and forming Aurora.
(Credit: ResearchGate ) 

Plasma is generally free of electrons and protons as you know, so when they interact with the magnetic field, the field lines change their path and take them away from our planet. But there are holes in Earth's magnetic field which locates at the poles and that is where some plasma makes through the magnetic field and to our atmosphere which you can see in the image above. We all know that our atmosphere is filled up with mainly nitrogen and oxygen. The energized electrons of plasma excite the molecules of our atmosphere and that causes the electrons of air molecules to go to higher energy states by absorbing the energy from the plasma and after that when the excited electrons come back to their stable state, they release energy in the form of light and in this case, that light is Aurora. It was Norwegian scientist Kristian Birkeland who unlocked the mystery behind the formation of Aurora Borealis.     

  

Electrons absorbing and releasing energy.
(Credit: SlideServe)   

Okay now, what is the reason between such beautiful colours of Aurora? That's different molecules. When plasma or solar wind interacts with nitrogen atoms they produce red and blue light, when they interact with oxygen atoms they produce red and green light. Now we know how Auroras are formed! By the way, the formation of Aurora depends on the shape of the magnetic field. It was Galileo Galilei, the famous ancient astronomer who named the northern lights as Aurora Borealis. Auroras that take place on the south pole are called Aurora Australis. 

Thank you.

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Published by: Prithul Das