Everything you need to know about the Auroras - VastlyCurious

    Every second about one million tons of matter are blasted from the sun at the velocity of several million kilometres per hour and some of it is targeted at our planet. Some of these particles are shielded from entering the Earth by our magnetosphere and some of them enter through the poles and react with the upper atmosphere. The amazing views of the auroras are often seen in the northern hemisphere. People over the centuries have witnessed this vibrant light show and couldn't figure out the cause of this phenomenon. So what are these Auroras and why do they occur? Do they occur on other planets too?

The Sizzling view of Northern lights in Alaska

What are Auroras?

    The Northern and Southern Auroras, which are also known as the Aurora Borealis and Aurora Australis respectively occur because of the high energy particle emissions from the sun. When these particles react with the neutral atoms in the upper atmosphere, they produce a spectacular light show which has amazed humanity for several centuries. This Dazzling light exhibition is done with the help of the free electrons from the sun and the oxygen and nitrogen atoms at 30 to 300 kilometres (18.6 to 186  miles) above the surface of the Earth.

    

    The Oldest identified report of an aurora dates back to 2600 BC as the images of the auroras are carved in the cave drawings in China. Norwegian Astronomer Kristian Birkeland was the first to find the proper explanation of the formation of the aurora. The Auroras can alter their colour and shape as the magnetic field varies. The Auroras appear to be constantly moving because the particles of the sun are running across the earth's magnetic field. The northern auroras are more popular because of their location, the northern auroras can be viewed from Greenland, Iceland, Canada, Norway and Russia, but the southern lights can only be viewed from the icebergs of Antarctica. 

Aurora Borealis or the Northern lights

Why do the Auroras occur?

    At the centre of our Earth, our hot molten core roils around under incredible gravitational pressure and this enormous pressure on the iron core shoots out a magnetic field around our planet. And that is how our magnetosphere formed which protects us from harmful cosmic radiations. But that is not always the case as the sun's particles which is in the state of plasma has high energy particles which have the capacity to pass through our colossal magnetosphere. These high energy particles are often emitted from the sun at high speeds which are called solar winds or Solar Storms. 

    The protons and electrons, which causes the Auroras on Earth, takes off from the outer layer of the sun's surface also known as the Corona. The Corona is the sun's hottest layer and hence the intense heat on the surface causes the vibration of the atoms. This vibration blasts off free electrons into the space at tremendous speed. This group of electrons forms plasma because of the intense heat and they are called the Solar wind. But in some cases, the sun suddenly blasts off massive balls of plasmas called Coronal Mass Ejections also knows as CMEs.

The Magnetosphere around the Earth protecting our planet from the sun's coronal ejection. Source: NASA

    Even though most of the coronal mass ejections from the sun are blocked off by our magnetosphere, we aren't lucky all the time. Some particles get through our shield where the magnetosphere is weakest which is at the poles of the Earth. These high energy electrons react with the oxygen and nitrogen in our upper atmosphere and excite them by transferring energy. To remain stable, the oxygen and nitrogen atoms release some of this energy in the form of photons (light particles). Depending on the altitude of the particles and the amount of energy, different colours are emitted forming these stunning Auroras.

Vibrant Auroras

    The Colours of the auroras depend on the energy of the electron and the excited atoms (either oxygen or Nitrogen). The Excited oxygen atoms give off the greenish-yellow colour and the excited nitrogen atom emits blue colour. The Combination of these colours in the atmosphere produces a blend of different colours like purple and pink. The Auroras are not always visible during the morning as the sunlight dims the view of the Auroras and so viewing the vibrant Auroras is ideal during the nighttime. Some atoms actually emit the photons in the form of ultraviolet light which can't be view in our naked eyes. The Auroras doesn't only produce a lively light show, but sometimes a crackling sound is also heard during the auroras.

Several spectra of lights visible in the North poles

    Although most of the Auroras occur in green colour, that is not always the case. Sometimes the oxygen atoms at higher altitude, they react with the high energy electrons and emits red light and at lower altitude, they react and produce green light. The nitrogen atoms will emit a different spectrum of light ranging from the colour violet to pinkish-red based on the elevation of the nitrogen atoms. The Auroras are also found to be asymmetric as some intense spots of lights were spotted in the north poles sometimes. The Auroras are often found at an altitude of just 80 km (49.7 miles) which is likely in purple in colour.

Do Auroras happen on other planets?

The Auroras on the south pole of Saturn. Source: NASA

    Auroras do not only occur on Earth but also on other planets in our solar system which have a strong magnetosphere around them. The Auroras are often spotted in the planet's magnetic poles in the planets like Mars, Jupiter, Saturn, Uranus and Neptune. We figured out the auroras on other planets like Saturn and Jupiter with the help of the Hubble Space Telescope. The formation of auroras on other planets is also due to the Solar winds. Although the smaller planets and even our moon don't have auroras because of the absence of a proper atmosphere. So a planet with a sufficiently dense magnetosphere is likely to have an Aurora around it.