Auroras are a phenomenon humans have been marvelling at since the beginning of time. Also known as Polar Lights, or Northern Lights (Aurora Borealis), these are beautiful bands of light streaking across the sky, formed predominantly over the Arctic and Antarctic regions, at high latitudes.
To understand how the aurora is formed, we need an understanding of the Earth’s magnetic field, and solar radiations, called solar wind. The magnetic field lines of the Earth erupt out of the poles and loops out, culminating back again at the opposite pole.
The charged particles surrounding the Earth – protons and electrons, when in a magnetic field, move along the magnetic lines of force. These electrically charged particles accelerate along the magnetic field lines into the upper atmosphere, where they collide with gas atoms, causing these atoms to emit light due to excitation. These auroras are powered by solar wind.
The Sun also has an atmosphere and a magnetic field that extend into space. The Sun’s atmosphere is made of hydrogen, and these particles are constantly boiling off the Sun and streaming outward at very high speeds.
This solar wind is always pushing on the Earth’s magnetic field, changing its shape. This squeezing of the Earth’s magnetic field requires a lot of energy. This compressed field around the Earth is called “magnetosphere”. It is stretched into a long tail, called magnetotail, which points away from the Sun.
When the space conditions are right, the build-up of pressure from the solar wind creates an electric voltage between the magnetotail and the poles. This causes the electrons to speed towards the poles with huge speeds. These speeding electrons collide violently with gas atoms. This gives the gas atoms energy, which causes them to release light.
This light may be of different colours, depending on the gas atoms. Oxygen emits green light at common aurora altitudes, and that is the most commonly seen colour. They occur usually in the Northern and Southern pole, and the main reason why they cannot occur around the equator is because the charged particles are spread out and not clustered together as they are at the poles. As a result, there are not enough particles to hit the gas atoms in the atmosphere to produce auroras.
These auroras dissipate the deadly energy of the charged particles powered by the solar wind before they reach us, thereby protecting the Earth from doom. The formation of these spectacular auroras is not confined to the Earth alone. They have been observed in Mars, and on Jupiter, where they occur on a much grander scale than on the Earth!