Lifestyle, Ludotheque, Okology

The Northern Lights: when the sky is steeped in colour

To classify by colour is human: the Europeans are called “white”, when they are closer to pink, the Africans are called “black” instead of brown and the sky “blue” when it can be green or pink.

Iria Leirós Pérez

Yes, pink, and although not everybody can appreciate this gift from nature known as the Aurora Boreal, part of England has been so graced, bearing witness this year to a peculiar phenomenon during which the sky becomes a festival of lights and colours.

An Eskimo legend tells how, “the limits of the earth and sea are bordered by an immense abyss, and lying above is a narrow and dangerous path leading to the heavens.

The sky is a great vault of solid matter arching over the earth. Within it lies a hole which spirits can use to pass through to the true heavens. Only spirits that have died a voluntary and violent death, and crows, have travelled this path. The spirits living there light torches to mask the prints left by the new arrivals. This is the light of the aurora. They can be seen there celebrating and playing games with the skulls of walruses”.

This legend, like so many others, opens a window to the imagination and leads us into a world of fantasies. But here in the present and advancing into the 21st century, science tears down these fantastic theories with irrefutable data and concrete terms that nonetheless cannot destroy the illusion and astonishment they create.

But, what are the Northern Lights and how are they are produced?

The Northern Lights, the popular name given to the Aurora phenomena, occur between October and March and are generally visible from countries such as Scandinavia and Iceland.

The name derives from the Roman goddess of dawn, Aurora, and the Greek word  Bóreas, which means north.

The sun, located 150 million kilometres from the Earth, is continuously emitting particles as part of a process known as solar wind.

The activity of the Sun sends Earth a great quantity of energy charged with electrons. These particles travel at a velocity of between 300 and 1000 kilometres per hour, thus covering the distance between the Sun and Earth in two days.

The Earth has a magnetic field that acts as a shield and is able to protect it from all this solar energy and allows the particles to flow with a certain tranquillity.

But sooner or later the accumulated energy has to be set free and a “magnetic storm” is produced that pushes this energy towards the Earth’s poles which, once in contact with the atmosphere, produces this feast of colours.

These solar particles collide with atoms and molecules in the Earth’s atmosphere (oxygen, atomic nitrogen and nitrogen molecules), which are found at their lowest levels of energy.

The energy that these solar particles carry disturbs these atoms, pushing them into “states of excited energy” and in milliseconds the atoms reach a point where they are filled to their maximum energy capacity and return it in the form of light.

The inhabitants of Iceland can see them nearly every day.

The colour of the Auroras depends on the atoms and molecules that the solar wind excites and on the energy levels that they reach.

In this way the yellows and the greens are sparked by contact with oxygen. Nitrogen produces a blue light and thanks to Helium we can appreciate colours in the sky as astonishing as purple or red.

Another legend tells us how, “the Boreal Auroras are the fruit of the love between two gods, one Roman, called Aurora, and the other Greek, called Boreas, who were so enamoured with each other that they gave expression to this love in the heavens”.

With the wisdom of science and thanks to investigations by NASA, today we can understand a little better this romance between Aurora and Boreas and the reasons that give rise to this beauty in the sky.

(Translated by Tim Huntington)

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