Can we make our own aurora borealis

Northern Lights: How Northern Lights are created

Per Helge Nylund works in the University of Tromsø's museum and researches the northern lights there. We asked him how the colorful stripes are created in the sky and we produced the northern lights ourselves

What is the difference between Northern and Northern Lights?

They are the same lights. Northern lights occur in northern latitudes as well as in the southern hemisphere. Here in the north they are called northern lights or Aurora borealis and at the South Pole they are called the Southern Lights or Aurora australis.

How exactly do polar lights come about?

The air kiss is a nice way to imagine how the northern lights are formed. The sun practically sends an air kiss to the earth, which becomes visible in the form of colored lights in the sky.

Because physically, the following happens: The sun emits a so-called solar wind full of energetic particles, electrons and protons and a little helium. This solar wind takes around 18 hours to reach the Earth's magnetic field, the magnetosphere. But the particles cannot get all the way to the surface of the earth because they hit the magnetic field lines beforehand.

These field lines are directed towards the north, i.e. perpendicular to the trajectory of the protons and electrons. This meeting causes the Lorentz force to act, which deflects the electrically charged particles perpendicular to their original path - and also perpendicular to the magnetic field. The solar wind particles are thus directed around the magnetosphere.

When the energetic particles combine with the earth's own atoms, the northern lights are created. Here above Tromsø they are mostly green, this color is created, for example, in connection with oxygen.

In order for us to see them, we also need a dark and clear sky. Because this reaction, which I have just described, takes place at a height of 100 kilometers, that is, far above the cloud cover.

Why can't we see the northern lights everywhere?

The earth's magnetic field is not circular like a ball, for example, but rather looks like an apple, with openings at the top and bottom. The magnetic field is traversed by magnetic field lines. The electrons are particularly attracted to these openings due to their magnetic charge and are directed to the poles by the magnetic field lines.

There they collide with the earth's own atoms. The northern lights are visible at both ends of the world at the same time. When we see the Northern Lights here in Norway, we can be sure that the sky over the South Pole will change color at the same time.

Why were people sometimes afraid of the northern lights in the past?

Even today, the aurora has not been fully explored. We have a physical explanation of how it comes about, but we still cannot predict it, for example. In the past, of course, people had far fewer opportunities to explore the northern lights than we have today. Since they did not understand what the northern lights are, they feared and respected them.

When the solar storms are very strong, auroras sometimes appear over central Europe. They are mostly orange or red. Especially in the Middle Ages, people thought a big fire was approaching or the light would prophesy war and bloodshed. My favorite story about it comes from Cornwall, England. During the Hundred Years War, people there saw a red aurora over the sea and wondered what it could be.

Someone then came with the public declaration that this could only mean that all of France was on fire and the enemy was thus defeated. Unfortunately it was just the Aurora and I would like to know what was going on in England when it became clear that France didn't burn down.

Why can you produce your own northern lights here?

The Norwegian physicist Kristian Birkeland made this experiment at the beginning of the 19th century when he was researching the formation of the northern lights. We refined his idea a bit and, in a box, recreated all the natural conditions that it needs to see the northern lights.

To do this, we have removed almost all of the air from the box; we only need a few oxygen particles to generate the light. Our little earth is a steel ball that is equipped with a magnet. So we already have an atmosphere and a magnetic field, now we still need the excess energy. It comes in the form of gas from our sun.

When we then press the button on the box, the sun sends out its solar storm and small but very clearly visible northern lights appear around the ends of the steel ball.

Links to aurora borealis and solar activity

  • Per Helge Nylund and the Aurora box can be found in the Tromsø University Museum. There is a permanent exhibition on the Aurora borealis and tours for children and adults. Between September and April, the Northern Lights appear in the sky over Tromsø.
  • You can find great photos of the northern lights on the website of nature photographer Bernd Römmelt.
  • On the website sonnen-sturm.info you can follow the northern lights in Sweden, Norway and Finland live via numerous webcams.

Photo gallery on the research ship "Polarstern"

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