For many years, people in the polar regions have been mystified by the dancing of bright lights in the darker months. This wonder continues today. But what are the northern lights, and why do they happen?

What are the northern lights?

Long story short, the northern lights are the visual byproduct of intense space weather. They are a natural phenomenon related to a multi-step process, similar in a way to lightning, rainbows, or even colorful sunsets. 

The things that cause them are primarily unseen, and occupy the space around us in our atmosphere. These are things like atmospheric gases, high powered electrons, and our geomagnetic field

The true wonder of all of this is that sometimes all of these things align into a moment of interaction- and when we are lucky, we can see the magic of auroras.

It all starts here on Earth

Earth is a special planet. It is one of the few places that we know of that can support human life. One of the many reasons that this is possible, is because we are protected from harsh space weather by our geomagnetic field. Many other planets also have a magnetic field, but ours is one of the strongest. 

The core of the Earth is filled with layers of partially molten iron under great gravitational pressure. This area of iron is huge, and because of the different temperatures, there is a fair amount of movement occurring here. 

The hottest material rises, causing swirling convection currents inside the Earth. You can see a current like this in a pot of boiling water. The way that those bubbles spiral up to the surface, is a lot like what is happening inside the Earth. The movement of all of this metal makes electrical currents that rise up through the Earth’s surface, and create magnetic fields. 

However, that isn’t the end of it! The Earth is also spinning, which causes additional movement in an effect called ‘the Coriolis Force’. This force combines all of those magnetic fields into one larger magnetic field, which protects all of us from radiation and solar wind, and forms the magnetosphere

Because we can’t see the magnetic field, we normally represent it by drawing lines. These lines go into and out of the Earth, meeting at the poles, making the Earth look like an exceptionally round butterfly.

what are the northern lights

From the sun, with love

So we know about Earth and its magnetic field. But where does the actual aurora come from? While the Earth is creating convection currents, a similar thing is happening in the Sun, a star that is nearly 15 million degrees Celsius at its core. 

As the pressure and movement within the sun push outwards, magnetic fields form here as well. The stronger ones are able to push through to the surface, slowing as they cool, and creating sunspots. We pay attention to these dark spots on the Sun, and often predict large auroral activity by their reappearance. 

But back to the action! The electrically charged gas (or plasma) that exits the sun contains the magnetic fields that were just created. When this massive “ball” of plasma breaks away from the surface, it is ejected out into space as a “solar storm”. (Smaller versions of this kind of expulsion happen frequently, and are often referred to as solar wind.)

Depending on the strength of the solar storm and the obstacles that it meets along its way, its speed and travel time can vary. That is why auroral forecasts are not always perfectly timed, it can be challenging for us to measure these factors.

The lucky collision

If everything lines up and the sun sends a solar storm in our direction, it will first have to pass over Mercury and Venus, before it gets to us. But when it does finally arrive, a strange sort of collision occurs between us and the solar storm. 

The magnetic field inside the solar storm clashes with our magnetic field, and combines. Once they are connected, the charged gases travel down the imaginary lines of the connected magnetic field, traveling to the poles that attract it. 

As the storm passes over us, these imaginary lines go with it, eventually breaking and reconnecting on the other side. This breakage creates another opportunity for gas to travel down to the poles, as the storm moves away.

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An aurora is made

The gases carried within the solar storm have arrived, and are traveling down to the places on our planet where the magnetic force is the strongest, the poles. But how does all of this make an aurora?

The gas that is now in our atmosphere contains supercharged protons and electrons, or ions. This energy becomes trapped in our ionosphere, around the north and south pole in a shape we call the auroral oval. 

When this happens, they will eventually collide with pockets of oxygen and nitrogen in our atmosphere- which is the big moment that we are waiting for. 

At the moment of this crash between ions and gases, energy is released that creates a glow, or an effect of visible light. You’ve seen many interactions like this here on Earth, like the interaction that creates neon light in signs.

This is an exciting moment, and a reminder of how small we are in the scale of the universe. But it is also only the beginning of the aurora’s visual journey to us, once it arrives. Because next, we have to learn about all of the Earth factors that have to line up and cooperate, for us to even begin to be able to witness this incredible natural phenomenon with our own eyes.