The burst of colourful light visible in the night sky is one of the most spectacular displays in nature. Now, research has revealed more about how these mysterious auroras are formed.
What is the aurora?
It is a display of light that can be seen near the poles in the northern and southern hemispheres.
In the north, the display is known as the aurora borealis, named in 1619 by Galileo Galilei. In the south, the lights are called aurora australis.
These northern and southern lights have fascinated and inspired humans for centuries. The Vikings thought the Northern Lights were a bridge to Asgard while the Maori of New Zealand believed the aurora australis was the campfires of previous generations.
So what really causes them?
The lights we see in the sky are created by activity on the surface of the Sun. Our star constantly sends heat, light and small particles out towards Earth. The protective magnetic shield around our planet protects us from most of this.
But some of these electrically charged particles travel through space at high speeds and are captured in Earth’s magnetic field before travelling towards the two magnetic poles. There, the particles react with gases in the atmosphere, resulting in stunning light displays.
Where can you see them?
The best places to see the lights are areas within the aurora zones. In the northern hemisphere, this includes Lapland, Iceland, Canada, Greenland and Norway. The Aurora Australis is much rarer – but it is possible to spot them in Tasmania, mainland Australia, New Zealand, Patagonia, Antarctica and even the Falkland Islands.
While these are the most likely places, the auroras have been seen in unusual spots. In 1859, for example, during a huge solar storm, colours were seen in Honolulu, just 21 degrees north of the equator. And astronauts on the International Space Station always have a good view as they live at the same altitude.
Why are they different colours?
Gases give off different colours when they are heated. The same reaction is also taking place in the aurora.
The two main gases in Earth’s atmosphere are nitrogen and oxygen. The green we see in the aurora is characteristic of oxygen, while purples, blues and pinks are caused by nitrogen. Very occasionally, the aurora appears red. This happens when the solar wind interacts with oxygen at a much higher altitude – and it only happens after very powerful solar storms.
Do they exist on other planets?
Yes! Any planet with an atmosphere and magnetic field is likely to experience the same phenomenon. Scientists have captured images of auroras on Jupiter, Saturn, Uranus and Neptune.
There have also been sightings of auroras on Mars, but because its magnetic field is different from other planets, the lights behave differently. In 2014, a spacecraft sent by NASA detected hugely widespread auroras in the northern hemisphere and almost as far south as the equator. “It really is amazing,” explains Nick Schneider, one of the team, “Auroras on Mars appear to be more wide-ranging than we ever imagined”.
What have scientists just discovered?
We have only known that the auroras are connected to solar storms for forty years. Even then, it was essentially just a theory. But this week, a group from the University of Iowa has managed to prove why the lights exist and how they form by recreating them in a lab.
Using the Large Plasma Device at UCLA, they recreated a miniature version of what happens between the sun and Earth. Professor Craig Kletzing said: “These experiments let us make the key measurements that show that the the space measurements and theory do… explain a major way in which the auroras are created.”
- Does understanding why the lights exist make them more fascinating – or less?
- Think of a new piece of folklore that explains why the auroras exist. Then write a story describing your myth.
- Aurora borealis
- Latin for Dawn of the North.
- Galileo Galilei
- An Italian astronomer. In 1633 he was found guilty of heresy for suggesting that the planets orbited the sun – rather than the Earth, as was generally believed.
- Aurora australis
- Latin for Dawn of the South.
- In Norse mythology, it is a location associated with the gods. In the Marvel Comics series, it is home to the Asgardians.
- Magnetic field
- Earth has a magnetic field extending from the planet’s exterior out into space.
- Patagonia refers to a geographical region that encompasses the southern end of South America, governed by Argentina and Chile.
- Mars does not have a global magnetic field that envelops the entire planet. Instead, it has umbrella-shaped magnetic fields that sprout from the ground like mushrooms. Experts say they are remnants of an ancient field that decayed billions of years ago.
- Large Plasma Device
- A research device designed to study plasma – a state of matter consisting of ions – atoms or molecules which have one or more orbital electrons stripped.
- Electrically charged particles
- These are also known as solar wind.