God used beautiful mathematics in creating the world.
- Paul Dirac
Aurora Borealis (From Pixabay- Image by Noel_Bauza)
WHAT MORE CAN YOU ASK FOR?
Envisage a night sky streaked with shades of colorful lights, dancing to a piece of mysterious music. Feeling dreamlike? This does exist in reality on our very own planet. I would literally not ask for anything more in life if I get to see this often :P Hope everyone wants to know what is this fascinating phenomenon. Get ready! Let's set foot in the dream. The Aurora/Polar Lights is one such magnificent phenomena on earth, created by mother nature. This luminous natural display is visible primarily in and around the polar regions. They are known as the Aurora Borealis (The northern lights) and Aurora Australis, in the south pole. The streamers of lights are mainly in shades of blue, red, yellow, pink, orange, and green colors. And that's amazing. They are produced in the ionosphere (the layer of the Earth's atmosphere that is ionized by solar and cosmic radiation. It lies 75-1000 km above the Earth.) when high-speed electrically charged particles strike the Earth’s atmosphere. Now I know that sounds like you are out of the dream. But let me elucidate how the magic happens.
WHAT REALLY HAPPENS?
To be precise, this occurs due to the 'Star of our Solar System'. Believe it or not, the sun is the primary reason for this spectacular display of lights. When we look at the sun, it looks like a small yellowish-orange colored ball. But it is actually a giant ball of fire whose radius is 696,340 km. Oh! What? Yeah, I get it. But this is the startling truth. Also, know that the surface temperature of the sun is a whopping 5,505 °C. It is unimaginable, right? Yeah, I was also surprised by the fact initially. Let the truth sink in and we shall move on. Let's talk more about the sun.
Our sun is a giant ball of plasma. It is a state of matter in which electrons get stripped from their atoms under high temperatures, creating an ionized gas. The sun's energy is generated through nuclear fusion in its core. I am sure we all know what nuclear fusion is. So let's move on. This energy is the light and warmth we feel on earth. Further, like the earth, the sun also generates a magnetic field, because of the electrical conductivity that the plasma creates.
WHAT DOES THE SUN DO?
Let’s first understand that the sun is not as quiet as it seems. The sun continuously blows out plasma that mainly consists of protons and electrons, into the interstellar space and this is known as the solar wind. This is one of the reasons for the formation of auroras. Once in a while, the sun also releases a cloud of high-speed plasma known as solar flares, which when comes in contact with the earth’s atmosphere, creates a spectacular display. When the amount of ejected gas is huge, it is known as a coronal mass ejection or CME. It takes around 2-3 days for a flare to reach earth. We are almost 150 million km away from the sun. Take a moment to realize the fact. The sun has more mysteries and astonishing facts than we can imagine.
Now you may be wondering how is a flare/CME generated. The sun might seem calm and quiet but it is a dynamic body, which is active all the time. As it’s surface temperature rises and falls, the sun becomes a bubbling body of energy. Sometimes magnetic field lines in areas of high magnetic strength (like sunspots) twists and turns and finally breaks off from the sun’s pull. When this happens, plasma particles escape the sun’s surface, hurtling into space with high speeds. This is the cause of flares and CMEs. Got it? Moving on, let's feel grateful for something that nature has created for us.
Formation of Auroral lights (Credit- Norwegian Centre for Space Weather)
OUR PROTECTION SHIELD:
Now that we have understood how the solar winds and flares are formed, let’s get an idea about the working of the earth’s magnetic shield or the magnetosphere, which protects us from the direct effects of the solar winds. As seen in the image, the earth acts like a giant bar of magnet and has a magnetic field surrounding it. Let us figure out what happens next. When the plasma ejected from the sun comes in contact with the earth’s magnetosphere after traveling around 150 million km (one astronomical unit), around 98% of the particles are deflected. A small fraction is funneled downwards to the earth’s poles since the magnetic field is slightly weaker at the poles.
HOW ARE AURORAS FORMED?
When the small percentage of energetic particles hits the earth’s atmosphere, the neutral atoms and molecules present in our atmosphere are excited. Due to this excitation of the atoms, lights of different wavelengths are emitted depending upon the kinds of atoms. Colors and patterns are related to the types of ions and atoms being energized and are affected by lines of magnetic force. Oxygen emits either a greenish-yellow light or red light and nitrogen generally emits blue light. Ah! That's awesome. Isn't it? Think of the process of light production in neon lights. Aurora formation is similar to it.
Next, this is something you ought to know. Auroras tend to be more frequent and fantastic during the period of high solar activity, which cycles over approximately eleven years (The solar cycle). Let's learn more about this in future articles.
WHY DO WE HAVE TO STUDY ALL THIS?
Sten Odenwald, author of The 23rd Cycle: learning to live with a stormy star says “Aurora is beautiful, but the invisible flows of particles and magnetism that go on at the same time can damage our electrical power grid and satellites operating in space. This is why scientists are so keen to understand the physics of aurora and solar storms, so we can predict when our technologies may be affected.” I think that one statement is enough to understand why this has garnered a lot of research interest. Great! Now let's see whether are we the only lucky people to witness such a marvel.
AURORAS ON OTHER PLANETS:
Unfortunately, Auroras are not only native to earth. They also tend to occur on other planets with magnetic fields, such as Jupiter, Saturn, Uranus, and Neptune, though they may be a little different than that of the earth since they are formed under different conditions. For example, Jupiter's auroras are a hundred times more energetic than those on Earth and don't radiate in the visible spectrum. Still, we are the only lucky species to witness it on earth as we are yet to discover an intelligent species on other planets. So let's enjoy our special presence until we find the truth :)
Aurora on Jupiter (Credit- NASA)
Though the basic nature and cause of the auroral lights are understood by researchers, the intricate connections between the sun and these lights are yet to be discovered. But nevertheless, we now have had a grasp of the reasons behind this marvel, and the next time we see an image of the aurora, we can have a scientific perception in addition to enjoying its artistic beauty.
WHERE CAN ONE ENJOY THE VISUAL TREAT?
The best places to see the northern lights are Alaska and northern Canada. Norway, Sweden, and Finland also offer excellent views. During periods of active solar flares, the lights can be seen as far south as the top of Scotland. The lights are always present, but winter is usually the best time to see them, due to minimal light pollution and the crisp air.
An interesting and fun to know fact is Astronauts orbiting onboard ISS enjoy close-up views when they fly through geomagnetic storms.
Aurora from the ISS (Credit- spaceref.com)
Resources: space.com, BBC, Wikipedia, NASA
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