Amanda Maxwell

Apr 8th 2022

What Causes the Northern Lights?


Visiting countries in the northern latitudes during winter is often a great opportunity to see the aurora borealis, or the Northern Lights. This awe-inspiring natural phenomenon is a beautiful addition to winter’s night skies, and many people plan holidays simply to view the flickering lights overhead. They may be natural, but they’re not always predictable. So, what causes the Northern Lights? And what’s the best way to make sure you see them on a holiday?

Shimmering Curtains of Dancing Light

The Northern Lights are one of the two aurora polaris phenomena visible from Earth. Focused around the Earth’s two magnetic poles, the aurora borealis shines out over the northern latitudes, while the aurora australis shimmers above the south pole.

The Northern Lights are seen on dark winter nights as curtains of shimmering colors. These include greens and blues, plus pink, red and purple. The lights often move or pulse as curtains of light. They are seen high in the atmosphere, between 100 and 300 km high (around 328,000-984,000 feet), but they have been recorded at heights of 600 km.

They are definitely strange phenomena to witness, and people often describe them as quite emotional to see. CBC News shares that Indigenous people in the north include the aurora borealis in stories of ancestors, connecting the lights with spirits moving and dancing across the sky. The lights are also visible from space. In fact, notes that astronauts aboard the International Space Station have shared photographs of the Northern Lights taken from above, showing a dancing necklace of greenish light surrounding the poles.

Upon seeing them for the first time, many people often ask what causes the Northern Lights.

Solar Wind and Charged Particles

Astronomers have a clear idea of what causes the Northern Lights: the sun’s influence on Earth’s night sky.

The solar wind generated by our closest star pushes a steady stream of charged particles toward us. The Canadian Space Agency describes how these protons and electrons collide with the planet’s upper atmosphere where they create tiny flashes of light with each collision. These collisions are what causes the Northern Lights in the night sky.

Incoming solar winds then interact with the Earth’s magnetic field, streaming the charged plasma flow toward the poles; this is where the light show takes place. The aurora is similar to rock luminescence as it’s also a reaction where charged particles from the sun react with atoms in the atmosphere to activate their electrons.

Aurora borealis activity is heavily dependent on solar activity. You’re much more likely to see the Northern Lights when sunspots are active, which occurs over an 11-year cycle.

What Causes the Northern Lights Color Spectrum?

Collisions between solar wind charged particles and Earth’s upper atmosphere create the lights, but the color of the light emitted depends on what the particles collide with.

For example, the Canadian Space Agency describes how pink and dark red forms when electrons collide with the element nitrogen. Collisions with oxygen at higher altitudes of around 300 to 400 km create red auroras, whereas green light is emitted at lower altitudes. Blue and purple fringes of light come from collisions with hydrogen and helium.

The best time to see an aurora is against a dark night sky, when the colors are easier to pick out. They’re simply not visible when it’s light, hence the best time of year for viewing in the northern hemisphere is between mid-September and mid-March.

Different Auroras, and Auroras in Different Places

The traditional aurora borealis shows as curtains of greenish light streaming down toward the ground. However, this isn’t the only type of aurora visible. Astronomers have recorded two additional styles of northern lights. One features horizontal frozen waves of light, which are called dunes. The other displays a streak of purple light and is often accompanied by a “green picket fence,” as a CBC Quirks and Quarks radio show once described it. This phenomenon is called STEVE, which stands for Strong Thermal Emission Velocity Enhancement, and it has been classified largely thanks to work by citizen science.

And there’s also often a difference between the auroras visible at each pole. Astronomers expected the light shows to mirror each other at Earth’s North and South poles, but when examined, they found that the activity didn’t match. According to Scientific American, this is due to the sun’s magnetic field impacting the tails of the Earth’s magnetic field in an unequal fashion.

And it’s not just peculiar to Earth. NASA notes that auroras are possible on any planet with an atmosphere and a magnetic field. They’re also visible on Saturn and Jupiter.

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