The formation of the auroras borealis. What are they?

Humanity has always been fascinated by the aurora borealis, or northern lights, some incredible light spectacles that illuminate with their colours the night sky. These events mainly take place on the Earth’s poles: on the north pole they are named auroras borealis (or northern lights), and when they take place on the south pole they are called auroras australis (or southern lights).

In this post, we explain how these great light spectacles are formed, what are their cycles, and we will make reference to the formation of auroras borealis on other planets of the solar system.

Formation of the northern lights

The Sun constantly emits electrically charged particles (or plasma) that travel through the solar system at an incredibly high speed. This constant ejection of particles is known as the solar wind. The solar flares (events that are not predictable) emit an enormous quantity of plasma.

When approaching the Earth, all these particles are attracted by the terrestrial magnetic field. However, before arriving at the surface, the magnetic field of the Earth deflects them towards the north and south pole. In these places, the particles penetrate the planet’s magnetic shield and make contact with the molecules in the atmosphere.

This contact with the different elements in the atmosphere creates these marvellous light and colour spectacles in various regions of the Earth.

A regular cycle

Every 11 years appear on the Sun what we call sunspots. They are dark zones on the Sun’s surface that have a thousands of times stronger magnetic fields than Earth’s. The sunspots tend to appear in pairs and can be many times larger than the Earth.

During the time they are present, the Sun’s activity increases strongly, that is to say, the Sun emits more plasma, and solar flares are more frequent.

In consequence, during these peaks of solar activity, the auroras borealis (and australis) on the Earth are more striking and frequent, due to the increase of electrically charges particles that arrive on our planet.

What causes the variety of colours?

The colour of the auroras depends on the particles with which solar wind interacts.

For example, The green and yellow colours are associated with the collisions with oxygen, while red, blue and purple are the result of interactions with nitrogen.

Auroras through the solar system

Auroras aren’t only limited to the Earth. In fact, a planet only needs an atmosphere and a magnetic field for creating an aurora. Other planets of the solar system, and possibly beyond it, also experience this phenomenon.

For example, the gas giants (Jupiter, Saturn, Uranus and Neptune) have powerful magnetic fields and dense atmospheres, that allow for auroras to form. However, as conditions are different on each planet, the auroras are different in every one of them. During the last years we have been able to photograph diverse auroras on every planet mentioned before.

An aurora borealis photographed on Jupiter

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