The Science of the Aurora

The British Science Festival 2016 in Swansea has just come to a close, with one talk at the Festival proving particularly captivating; Dr Melanie Windridge delivered a passionate and mesmerising talk regarding the science of the Northern Lights, also known as the aurora. This ethereal display of colour and light is often seen by those living at Northern latitudes and has been a dazzling source of wonder for centuries of humans. The aurora over time and different civilisations has created stories of spirits and been an omen of death and war – but what is the aurora actually, and how is it created?

The aurora originates from the sun, and the charged particles (plasma) that it throws out in all directions; this moving plasma is called the solar wind.

NorthernLights journey_short.020

On top of this, the sun sometimes releases more matter into the solar system in solar eruptions or giant Coronal Mass Ejections.

The sun throws out billions of tonnes of matter into the solar system which would be dangerous to our planet and all life on it – but the Earth’s magnetic field forms a protective bubble called the magnetosphere. Without this, the onslaught of the solar wind and coronal ejections from the sun would be like a plasma rifle shooting millions of highly charged particles at our planet.

Magnetosphere_whitebkgd

 

Most of the plasma is pushed away from our planet along the magnetosphere when it hits Earth, but the magnetosphere also gains energy from the solar wind. This causes the magnetic field pattern of the Earth to change – the ‘tail’ of the magnetophere is pushed closer and closer together until the fields break explosively, catapulting electrons to Earth. This process is called a substorm and is highlighted in the NASA video below:

When the charged particles hit the Earth’s atmosphere, they interact with the gases oxygen, nitrogen and hydrogen to create the spectacular light show we see – the Northern and Southern Lights.

When the electrons in the plasma collide with the gas in our atmosphere, they are ‘excited’ to higher energy states. They then lose this energy by emitting different wavelengths of light, which we perceive as the colours of the aurora. Oxygen usually emits a green or yellow light, whereas nitrogen usually gives off a blue light.

 

Dr Windridge is a plasma physicist at Imperial College London and has expedited to many northern countries in search of this beautiful phenomenon to study and learn about its causes. As a writer and storyteller, she has cultivated a collection of the stories that the aurora has created across different people in different stretches of time, each group viewing the aurora as something different, with varying meanings. You can find out more about her book, ‘Aurora: In search of the Northern Lights’, here. 

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