Aurora Borealis

Everyone has heard about the stunning Northern Lights, otherwise known as the Aurora Borealis. But what are they? and what causes this incredible display? There was a time this spectacular light show was believed to be some sort of sign from God or even a vast fire surrounding the ocean.  As other worldly as the lights may seem they are simply caused by charged particles smashing into the Earth's atmosphere.

The Earth acts as a giant magnet, and as such it produces magnetic field lines that encompass the whole planet. They help deflect any
charged particles caused by solar flares. Every so often the Sun's magnetic field lines get tangled up to such an extent that they suddenly "snap" and huge amounts of energy and charged particles are released. Of course, this wouldn't be a problem, except for the fact that they pose a great threat to Earth. Luckily, we may rest at ease because our planet provides a shield that prevents them from reaching Earth's surface.



The Earth's magnetic field lines are nonuniform so any charged particles heading our way get trapped, and spiral about the field, oscillating between the end points. These particles spiral from pole to pole in a matter of seconds. Most particles originate from the sun, but some come from other celestial objects. When they get close enough to the poles they collide with atoms in the atmosphere causing them to emit visible light. This causes the Aurora Borealis, visible in the north pole, and the Aurora Australis, visible in the south pole.

They vary in color depending on the excitation, and ionization of the atoms of Earth's upper atmosphere brought on by collisions with solar winds. The atmosphere is made up of oxygen, and nitrogen that when excited emit a photon of light. For instance, when an oxygen atom collides with a rapidly accelerating charged particle it absorbs energy, and then releases it by emission of a photon. Usually, oxygen emits green light because it takes three quarters of a second to emit. It can also emit red light, but this is uncommon as it takes about two minutes for oxygen to return to its ground state, and by that time the energy gained might be lost to  collisions with other molecules. Nitrogen, on the other hand, is known to emit blue or red light depending on whether it regains an electron after being ionized or whether it returns to ground state after being excited. There is also a color difference with altitude. In higher regions of the atmosphere there exists a greater amount of oxygen where red emission prevails, followed by oxygen green and nitrogen blue.


Usually the Auroras are confined to polar regions because that's where the charged particles get closer to the Earth's surface. Once in a while, Earth's magnetic field lines are distorted considerably due to a large number of charged particles entering the Van Allen Belts (belts of charged particles). As a result, the Auroras are visible in lower latitudes. Although they put on a good show for people in these low latitudes, they can cause power blackouts like the one in Canada in 1989.




So next time you find yourself visiting any of the poles keep a look out for these lights, and you might just be amazed!



*As a good side note: Auroras can also occur on other planets as long as it has a dense atmosphere.*