Science Behind Northern Lights

Aurora Polaris Cover

Northern lights are both mysterious and mesmerizing phenomenon of nature. Some people are fortunate enough to visit the places where they are easily visible and absorb such awe-inspiring events, while others myself included never got a chance to visit these places. Though in the age of such advanced technology we are able to recreate these lights via holograms, it just isn’t the same as the real thing. Plus it takes away that rush of being on a mountain out of nowhere just gazing at the sky full of magical lights.

What are Northern Lights?

Northern lights or Aurora Polaris is a natural phenomenon that occurs in both the northern and southern hemispheres of the Earth. It occurs due to the interaction between Earth and the Sun, not physically, thankfully. The way our Earth is created, it has molten iron at its core which is constantly under the pressure of gravitation, and as a result that roaring iron produces magnetic fields that cover the entirety of our planet and space around it up to 65,000 kilometers, and this field is known as Magnetosphere. Now the Sun comes into the play, as its surface is made up of plasma and it constantly keeps shooting these into the space. These highly charged electrons and protons are shot from the Sun towards the Earth in the form of Solar wind, while most of it is reflected away by the magnetosphere some manage to enter our atmosphere via the northern and southern hemisphere where magnetosphere is the least strong. When these electrons and protons enter the atmosphere they interact with nitrogen and oxygen atoms and they become excited, in order to balance out the charge, both nitrogen and oxygen atoms shoot out energy in the form of photons, resulting in the mesmerizing waves of energy, The Northern Lights. Funnily enough, in the past people thought it has to do something with deities.

Solar Wind for Northern lights

Earth’s magnetosphere deflecting the solar wind.

Visibility of Aurora Polaris

It is often a misconception that these lights are only visible at certain locations, it is not entirely true. These lights have been seen near the equator as well, additionally, they are not frequent in other locations compared to higher altitudes. On the topic of visibility, it is natural that these are barely visible during the day, as sunlight strongly overpower them, so the best place to gaze at these is during the night. Also, in some locations such as Alaska, they are visible pretty much all year round.

Shades of the Northern Lights

The color spectrum of the light is also a result of the interaction between the atoms and at what height they are present. As you may have seen from countless pictures, the primary colors for these are green, violet, and red with some slight hues of different colors. Before we know about these we must learn about the atmospheric layers of Earth.

Layers of atmosphere

Layers of Earth’s atmosphere.

  • Troposphere: This is where we live, with plenty of breathable oxygen and lovely weather that happens in this layer, it goes up to 10 km in height. The higher you go here, the cooler it gets.
  • Stratosphere: From the previous layer up to 50 Kms, the stratosphere exists and the savior ozone layer is also present here. Unlike the troposphere, the higher you go the hotter it gets.
  • Mesosphere: Another protective layer of the Earth, here the meteors burn up before entering our lower layers. Mesosphere goes up to 85kms and here the air becomes extremely thin, plus the air pressure decreases exponentially. The temperature near the top-end of this layer is about -90°c.
  • Thermosphere: This is basically the layer that separates Earth from outer space. There is a very thin layer of air present here which makes it fall under the category of Earth’s atmosphere. It goes from 90kms to 800kms. Satellites actually orbit the Earth in this layer and more importantly, the northern lights appear here.
  • Exosphere: As the name suggests, it is the outermost layer of the Earth’s atmosphere. Some don’t even consider it in Earth’s atmosphere as it goes from 1,000kms to 10,000kms. It is basically space.

Now that we know at what altitude the lights occur, let’s see why they produce such colors.

  • Blue: Blue along with violet are not common colors of these lights, as they only appear when the solar activity is high. These shades appear when the particles from the Sun interact with nitrogen atoms at an altitude of 90kms.
Blue aurora

Blue colored Aurora Polaris.

  • Green: Green is perhaps one of the most common colors, though it is not a specific green color as it appears in nearly all the shades of green. Here the color appears due to oxygens’ reaction with these particles at around 160-200km high.
Green Aurora

Green Northern Lights in the sky over Alaska.

  • Red: Again red is a rare shade of Aurora Polaris and only appears when the solar activity is high, maybe even intense than when blue tint appears. Above the altitude of 250kms when oxygen atoms interact with the charged particles the uncommon red shade occurs.
Red aurora

The rare red-colored Aurora Polaris in Colorado.

Though these are the primary colors, this phenomenon may also appear in the yellow, pink, or white shades as well due to combinations of the mentioned colors. This natural occurrence is truly fascinating and if given a chance one must gaze and absorb the beauty of these lights being fueled by the plasma of the Sun.


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